People keep asking the question, so why not compile a list of reasons?

FOR THE RECORD: I’m not asking for anyone to agree or disagree with these points. I’m simply making this reference list of so other people can understand what’s going on and why fans are upset to begin with. (Feel free to add to the list if I have left out/forgotten anything)

• Craig McCracken is not involved in any way whatsoever. (Supposedly according to Tom Kenny, Craig approved the show yet he has no control over what’s actually going to happen)
  
• Before the show was even announced, Cartoon Network asked back the original voice actors. Except for the girls. The voice actors for the girls were upset with this and were more than willing to voice the girls, and the network still refused to rehire them for the show. Devastating Tara Strong (Bubbles), Elizabeth Daily (Buttercup), and Cathy Cavadini (Blossom).
  
• This wouldn’t be so bad if they were giving new voices to the girls, but the new voice actors are trying to sound too much like the classic girls. So why even replace them?
  
• ALSO RECENTLY NOTED, they didn’t ask back Miss Bellum’s voice actress either, Jennifer Martin. 
  
• It has a very high-budget opening, yet the episodes and previews we HAVE seen are littered with animation errors and it just looks shoddy.
  
• A fan re-animated the clip from the episode animation above with no budget and it looks better.
• It seems very likely that the reboot was made only to sell toys, not re-invent or continue the story of the girls. So they don’t’ care much about quality. This is due to the large amount of merch already available despite the show not even being out yet.
  
• The first episode, “Man Up,” has the exact same plot of an episode from the original series’ 5th season, “Makes Zen to Me.”
  
• Same first episode gives a grossly stereotyped version of “Zen,” and is full of really cringy mis-representation among other issues. (This user explains it very nicely, as well as tears into other things wrong with the episode)
  
• Same first episode used a stock photo of a desert for one of the backgrounds. It can easily be found on google images. Continuing with the theme of shoddy quality.
  
• Buttercups’ voice actress, Natalie Palamides, described her character’s personality as “thick skinned” yet the first AND second episodes of the reboot already contradict this (She flies off the wire and beats up a character for calling her “princess” and the goes on to hurt her sister). It makes a lot of people concerned when not even the voice actresses understand the direction of their characters
  
• The girls’ personalities are all over the place in general, and in many ways aren’t true to who they were in the original. “Flanderized” is a good way to describe it.

((On a side note,  it’s been officially stated the reboot is being made with older audiences in mind as well. It’s not just “for kids.”))