Mallard duck, domesticated but living in a wild duck pond wont fly?

We had mallard duck who we raised from a baby with our 6 chickens. we fed it chicken feed but it doesnt have angel wing. we couldnt keep it so we released it in a pond near an apartment building with a bunch of other ducks. i dont need lectures on that right now all i need is an answer to my question. it is quite fat and healthy but doesnt fly. it is a male mallard. all the other ducks go sleep somewhere else during the night, our duck sleeps alone in the middle of the pond. Why? it can fly i saw it fly a few feet once to get into the pond. does it just not want to?