Seasons 1 - ~17 of South Park humored the shotacons in its audience so much that it genuinely shocks me when people question why Japanese fujos latched onto it. Isnt it obvious? The show's premise is little boys doing crude and sexual things!
>countless "jokes" where the humor hinges on its little boy characters being graphically sexually abused (including a scene were Butters gets anally raped by a machine, several episode where Cartman is anally probed by aliens, lots of nods to Butters being molested by his family members, etc), which are never NEARLY as graphic when they are applied to girls
>tons of nods to niche pederast culture, to the point where they have Craig refer to himself as a catamite and a whole episode on NAMbLA (an organization so obscure to straightoids at the time that a lot of people think South Park invented it!)
>plenty of scenes were shota butts/chests/feet are displayed for the audience to look at
>open acknowledgement of the shotacon fanbase during the fujoshi episode
Old South Park was, at "best", a show that appealed to people attracted to young boys without doing much to stop it, and, at "worst", a show that actively pandered towards those sort of audiences. If the artstyle was MARGINALLY less stupid-looking, this would be totally undeniable. But, because it's so silly, Tremato were able to get away with all of this for years.
I mean, the creators are LITERALLY Jewish libertarians. Come on, guys.
Somewhere in the process, the writers fell out of love with the boys and started writing near-exclusively about the lives of the unfunny, boring adult self-inserts in the cast, which is why SP stopped being funny, and why it's so lame today.