1. Cloud had a distinct reason to be attached to his outfit. 2. We have no proof he never changed at least for a second while Tifa washed it for him. 3. Cid's outfit only exists for at most a few weeks in-game time. 4. At least characters from Spira have a good reason to wear the same outfits consistently: I doubt they have much in the way of fashion designers to nag them into wearing new clothes everyday. The closest thing they've got to changing clothes is the Garment Grid.