>>56453004I'm guessing that Gardevoirs remove their dresses whenever the following circumstances happen:
1: It gets very warm and they undress to cool down.
2: They're about to take a bath or a shower and have to undress so that their dress doesn't get wet.
3: During the beginning of a mating session, Gardevoirs (Particularly females) sometimes willingly undresses in front of their partner to get them aroused.
4: They just prefer going around naked for a while. (Nudism)
Same logic can actually apply for other Pokémon that wear clothes, such as Meloetta.