Second, they use a lot of regular voice actors. Ignoring for the moment Jim Cummings and Frank Welker, whose versatility puts them in a lot of films, recent Disney films have included such veterans voice actors as Keith David, Nicole Sullivan, Brad Garrett, Tom Kenney, Ron Perlman, and Maurice LaMarche, among others.
Frozen only had ONE professional voice actor in it (I'm not sure if Alan Tudyk counts or not), Maurice LaMarche. And he only had a few lines. Wreck-It Ralph, to be fair, had three: Jess Harnell, Maurice LaMarche, and John DiMaggio. But again, they weren't major characters.
I don't mind the casting of celebrities as the characters in Disney film. But there isn't really any need for it.
Also, what Disney movie had Nicole Sullivan in it?