Becuase alot of the shows that you see like Gumball, Steven Universe, TTG, alot of the creators of the show went and attended CalArts.
Despite that most of them never shared classes and yet all popped out similar styles that are very simplified . Thats how it got its name
Alot of people who go to CalArts and don't make shows also pop out very similar looking styles. These are usually Tumblr/Twitter artists