iron Man flies by using boot jets.
Thor flies by hurling his hammer and being pulled along after it.
The Vision flies by a directed application of the anti-gravity mechanism within his android frame.
The Wasp flies by using her tiny wings.
There are and can be different ways of doing the same thing, and each one comes with their own conditions. The Wasp will eventually get tired. Iron Man’s jets will eventually run out of energy. And so forth.
This is how that particular story works.