Vector puppet animation and a shocking drop off in investment in kidvid is largely at fault, but international marketing is also to blame.
What's important to remember is that the whitewashy approach to character design in kidvid is a backslide.
Representation in cartoons had generally been on an upswing since the 1980s, even though efforts were often minimal, clumsy, or badly executed. Diversity helped sell action figures in the lucrative US/Canadian market and it was recognized as a prosocial value on the production side.
"Prosocial messages" are a major part of kidvid TV pitches and development, nearly every show has specific prosocial lessons the narrative themes are intended to work around, even if its an action-figure ad. These range from sincere expressions of the creator's intent (Gargoyles, OG Magic Schoolbus, OG He-Man (no, for real)) to the entertainment equivalent of carbon credits.
Slight aside. Actual ink-and-paint animation tended to lock characters down into more distinct tones because there were only so many standard paint colors. Which is why Kwame from Captain Planet, Roadblock from GI-Joe, and Tim from OG magic schoolbus all use essentially the same pantone.
Ralphie gets skinny because not only fatphobia, but I suspect because he would need slightly different rigging and would add just a teensy bit to the budget adjusting his animations when they could just copy-paste from one of the other identically built kids. If they need to put them all in spacesuits or diving suits or whatever, they just make the one body and slap the heads on, eazy-pezy.
Decals on the schoolbus mean they have to be tracked, they have to use different versions of the bus in flipped shots, same with Mrs. Frizzle's clothing patterns. Wouldn't want to spend time flipping Ralphie's "R' around.
And with the marketing for everything now being global, there's an impulse to average everything down to appeal to all markets to a general degree. Making stories oversimple makes them easy to translate. Humor varies culture to culture, keep it slapstick or quick quips that can be localized easily. Everything that makes the Chinese censor boards happy also makes US reactionaries less likely to kick up a protest, the incentive is to keep everything:
ALSO: These characters have the same face. They probably use the same eye and mouth parts for character animations.
It's all to do it as cheap and broadly appealing as possible, as determined by business weirdos who know nothing about art and care nothing about kids, and they're more than willing to leverage racism (or just ignore that its happening) for the promise of a tenth of a percent more profit.
And what's galling is that this kind of animation software doesn't have to make crap. It can be used to make amazing stuff and still be vastly cheaper than traditional hand-drawn, but the same quality at 60% of the cost is never going to beat 1/2 the quality at 5% of the cost for the money-men.
The path of least resistance rolls over a lot of people.
