Three factors: Color, personality, and realism.

First, color and shading.

vs.

The predominant style of the day in anime employs very crisp cell shading and eye-watering colors. Both female and male hair and eye coloration comes in any range of colors, from neon to pastel to white (although female characters most often display this). The typical color for skin in anime has gradually lightened to almost pure white over the years. Additionally, modern anime has a very specific, hard method of shading and highlighting that makes hair and skin look unnaturally shiny and often gross, lowering the realism value and throwing the texture of the skin into uncanny valley territory.

Secondly, anatomical proportions. Besides the shading, female character body and facial proportions have degraded so much that they are barely caricatures of human anatomy. Here are some examples of female anatomy in early anime:

and some in modern anime:

The biggest changes have been to the breast to waist proportion. For some reason, anime producers believe that an E-cup is the appropriate cup-size for an average 14 year old Japanese female. Bodies have also lost all of their depth (that come from an illusion of thickness necessary to two dimensional media) in favor of being skinny and flat (except for voluminous breasts, of course) and many normal, attractive parts of ladies (ribcages, stomach pooches, and natural folds) are simply smoothed over. Another noticeable change has been to the eyes and facial shape. Anime noses and mouths are apparently inversely proportional to eye shape, size, and distance apart. As the size of the eye increases, shape becomes more prominent, and distance towards the ears increases, the size of the nose, mouth, and chin decrease, contributing highly to the uncanny valley effect many modern any girls have.

Take these faces:

vs these

Thirdly, anime girls have lost much of their visible personality over the years due to moefication. This has happened to male characters also, although to a lesser extent. Anime girls are often not allowed to make cartoonish expressions (deemed unattractive) or generally change their expressions at all barring blush lines. In producers’ efforts to make the girls attractive to the audience in every frame, they sacrifice any personality that they might have. Anime girls look increasingly similar to one another, differentiated only by their hair style and eyes. Granted, there has always been a problem with female character same-face syndrome since the conception of anime (actually, in all drawn media) but as the number of female main characters in anime has grown, ironically, the problem has only increased.

Wow! Anime girls with the same hair color that you can actually tell apart!

And somehow, girls with all different colors that you can’t.

The screenshots in this post were taken from Urusei Yatsura, Neon Genesis Evangelion, Nadia: The Secret of Blue Water, Ranma ½,  Kimagure Orange Road, Ping Pong Club, One Piece, Angel Beats, Higurashi When They Cry, Sword Art Online, Shakugan No Shana, and Chobits. The examples above were not used to bash any anime, but merely to demonstrate the evolution of anime art tropes from the 1980s to now. The writing and plot of each anime were not taken into account at all.

#this is also a good addition#but lets not forget that the newer styles is also pandering to pedophiles#hence why they often look younger regardless of how old they are

Literally every “modern” example besides Keijo is at least a solid 5-10 years old, modern anime has issues but damn if this isn’t biased and cherry picked to hell

Because I’m a petty bitch and happened to find this again while looking for something else, lets actually do a counterpoint. To start off, let me say I don’t really know pre-2000s anime very well, I’m not out to say that anime now is better than in the 80s/90s because I don’t know enough to compare. In fact, I’m not going to talk about 80s/90s anime at all, as I’m only here to defend modern anime. It has been painted here with a much broader brush than I think is fair.

Let’s start with addressing the idea of sameface syndrome, something even OP acknowledged isn’t new. Do all modern anime have casts of female characters that have the same face just with different colors and hairstyles?

Because one of my big issues with OP’s examples was that they were all rather dated, lets date these. My Hero Academia (2016), Little Witch Academia (2017), Seven Deadly Sins (2014), Attack on Titan (2013). Some shows, like our two “Academias,” provide variety with cartoonishness, their non-realistic premise allowing them to be more loose with what “makes sense” or is “possible.” With SDS you might argue individual features are similar, but the body language and expressions communicate unique characters. (More on character expression in a moment.) And then even in more realistically styled shows like Attack on Titan,  you can easily tell all these women apart because their features and expressions differ.

I’d also like to specifically talk about OP’s point of three redheads from 80s/90s anime having the same hair color but being clearly different characters. It’s not really that impresive that three women from different anime with wildly different art styles would be easy to tell apart. Anyway, here’s three women with the same hair color from the same anime (Fullmetal Alchemist: Brotherhood, 2010) that you can easily tell apart.

(Honestly is there an 80s/90s anime with as many strong, fully realized, and varied female characters as FMA because I would love to see it)

OP also claims that female characters in “modern” anime do not have the same variety of expression as they once did, forced to only make expressions that make them cute and pretty, definitely nothing overtly cartoonish that might ruin that. Let’s look at a couple modern anime girls.

Samurai Champloo (2004), Gekkan Shoujou Nozaki-kun (2014), Welcome to the Ballroom (2017). Definitely, a variety of expressions, many of which aren’t especially pretty, because they exist for comedic effect. These are girls whose moods and personalities are shown in their expressions, as any character in a visual medium should.

And lets not forget;

just like literally all of Kill la Kill (2013).

Bonus: This is technically from the manga but the anime HAS started this season, so; Asirpa from Golden Kamuy because it would be wrong of me to talk about cute anime girls making insane cartoon expressions without her.

Lastly, I’d like to talk about the one thing I don’t necessarily disagree on, the trend towards girls more uniformly being drawn as young and petite but large breasted. I am the last person who’s going to argue that there aren’t prevalent anime styles that focus on sexualizing and objectifying young women and girls. So here’s a couple of designs that strike me as especially counter to that trend.

Kids on the Slope (2012), Fullmetal Alchemist: Brotherhood (2010), Gangsta. (2015, both of the last two)

Now, obviously I’m picking examples that fit my case just like OP did, but I’m not here trying to make ultimatums that one decade of anime is one thing. I’m not going to sit here and try to argue that shows like Higurashi and SAO aren’t bland waifu garbage because they absolutely are. However, I’m also not going to sit here and act like they invalidate all anime made after an arbitrary dateline. I’m certain there was shit anime in the 80s and there’s shit anime now. It feels like more because there is quantifiably more anime being made now than there was back then, and you really can’t make broad sweeping statements about it as a genre because there are so many different shows out there. Even between 2006 (when Higurashi and Haruhi came out) and now, is vastly different. It doesn’t sit well with me for all “modern” anime to be dismissed on account of shows that I knew were poorly rendered when they came out 12 years ago, especially when I know there’s so much out there that is so much better.

For the road, please take this very good picture of Chain Sumeragi (Blood Blockade Battlefront, 2017)