It's where the Day Campin' pin trading event will be held on the 21st of this month.
Disney needed an area like the for large (and yes, corporate groups). Same goes for the Hollywood & Dine building in DCA. It gets good use for events.
Truth be told, yes, live entertainment isn't cheap - especially in a big venue of any kind with a big staff onstage as well as behind the scenes. As popular as a show may be, all that time with guests sitting in one spot isn't the best way to enhance revenues. And we all know that the Accountanteers want more money out of guests every day...
But give credit where due as well. Shows like Hunchback at the Festival of Fools and others in the Fantasyland Theater/Videoplis did show Disney that full fledged Broadway shows would be popular enough to support audience interests.