Because let’s get real here, Heinz had it out for a LOT of people who screwed him over, from Hot Dog salesmen, to baking soda volcanoes, yet in NO episode in the series did he ever say ANYTHING negative or acrimonious about his ex-wife. Never tried to screw her over, never battled her for more custody of Vanessa, he respected her dearly and never saw her as an antagonist, just someone he grew apart from emotionally. GRANTED he still bled her dry with alimony checks, but hey she’s loaded and she didn’t seem to mind.
Like, once or twice they reference reasons they didn’t get along and he sometimes references her meanly in songs (mostly just to get a rhyme) but they’re generally both totally cool with each other. Like, they have a very amicable relationship for exes and I think that was good to portray on a kids’ show, doubly so because Heinz is often an unreasonably petty man and yet Charlene is never someone he feels “wronged” him (as compared to, say, the girl who bullied him in Gimmelschtump as a form of flirting or the woman who left him for a whale). Like, the most he’s done with lightly bicker with her about picking up their daughter when he’d planned to do something else.
And this pretty much HAD to be a conscious choice by the writers. Like, Heinz goes after almost everyone at some point and him not going after his ex was clearly something they made their minds up on.