Liberalism.
PC attacked "violence" in Tom & Jerry and Bugs & Daffy cartoons starting in the 1960s. By the 1970s ACT (Action for Children's Television) had worked over the story development sessions. The woman behind it was forced to watch the pablum and said that it may be boring but at least it wasn't offensive.
SeeBS tried doing "news breaks" (IN THE NEWS) in the 1970s to propagandize to the growing chil'run.
By the 1980s, toy companies created programming up around their wares (rather than the other way around).
Then NBC started to make s(h)itcoms aimed at teens and pre-teens since there were better rerun syndication opportunities for live-action programming than animated shows.
Eventually Today added Saturday to their lineup (because kids SO much want to watch grownup shows and grownups SO much want to wake up at 7am on Saturdays to watch the lib-news infotainment they see all week long).
It's been winnowing down for awhile.
And the war on sugar cereals may have been the death blow.
This is not the country I grew up in.
It was claimed that Lee Harvey Oswald liked the “violent” cartoons on TV.
That, some claimed, was why he shot John Kennedy.
It got worse after Bobby Kennedy was murdered. All TV shows immediately dumbed down to kiddie levels, comic books got changed, paper back books removed their lurid covers. Movie producers said they would police themselves with a rating system and began to churn out the most bloody vile movies possible.