I have read that besides having to pay a person to wear the suit and a helper, all the costumes require daily up keep and that costs money. I have heard this is one of the reasons for limited Fantasmic showings. Also I guess there is only so much space.
All the characters from all the movies can't be out.
I'm sure when Up replaced Bolt there were Bolt fans having the same complaints and the same when Bolt replaced Wall-E.