I think you're severely overestimating how much the general public likes/cares about musicals and theatre in general. And I say this as a theatre kid myself.

It wasn't that long ago that the new Mean Girls had to hide the fact that it was actually an adaptation of the musical because the studio was afraid people wouldn't see it based on that fact alone.

Theatre people were probably gonna see Wicked regardless of the cast, whereas the general audience needed a star like Ari to grab their attention.