There is a simpler reason that they use CalArts for most of the major, mainstream shows: Its cheap and can be cranked out extremely quickly. Because Disney has declared that their strategy for keeping people watching their stuff is quantity over quality, so that necessarily means cheap, rapidly produced cartoons....that then get no one to watch it, or get invested enough to watch it long term. Which is why Disney is now running into money trouble and may have to start screwing with Disney+ to keep it from going bankrupt.