Just some coach's philosophies, that's all. Happens so rarely, is it really worth devoting a bunch of practice time to it since time is limited? I think that's what it boils down to.
Sure there are outliers. There are in anything. Mugsy Bogues was only 5'4" but you don't see college coaches beating down the doors of 5'4" players do you?
Who said anything about devoting a bunch of practice time? Working in a few glove flips during fielding skills work isn't a big deal. If you don't like the idea, don't include it. Personally, I think it's a valuable enough skill to give it a little time.