Some people like a lighter weight and different grips. Lots of cases have a kickstand where you can prop up the deck and use your favorite controller.

I’d guess it is because the most popular way to acquire games for Citra was Nintendo’s own servers

Hell I usually limit games to 45 or 30 if they happen to run 50+ on the Deck. Not because I don’t notice a difference but because “what if I can’t charge my Deck for some reason?”.