I'm Gen X, and I'm a little taken aback by the heavy emphasis on the cartoon characters, as I really don't consider that cartoon to have much to do at all with the D&D game. It was a popular children's cartoon from 1983-85. It came and went. 95% of the characters in it never really appeared before or since that two-year period, until Wild Beyond the Witchlight (2021) and a Brazilian car commercial. It just doesn't feel like a particularly key or seminal part of D&D history to me. It's not "the beginning of D&D". It wasn't the "peak" of late 70s-early 80s D&D popularity (probably 1982). It just wasn't, tbh, a defining moment for the game.
It would feel fine to me to have ONE character from the show on the cover of the DMG. THREE - and no characters from any other sources - feels weird. Not the crime of the century, but feels like an odd choice to me.
I also watched the cartoon occasionally as a kid (I would have been age 7-9 when it aired) and didn't care for it. I was reading The Hobbit and watching Doctor Who at that age, so the cartoon just seemed kinda simple and dumb (and I know that makes me a child snob). So even though I'm exactly the target demo for the cover, it just doesn't resonate with me.
That said, the actual reason I don't like the cover is strictly because of the art style. I do like the interior art from the new PHB that features the kids from the show in a discernable dungeon entrance setting that looks like it could happen in a D&D session.