I suspect they are not at all committed to their faith but while they can get away with tight clothes and make-up, there is no way their families would accept them not covering their hair because there is a specific religious edict against that (no concerns about Spandex in the dark ages). As you say though, it's completely ridiculous because the purpose of the hair covering is to reduce attractiveness and they are circumventing that aim in other ways.
When I was on holiday once I remember a young Muslim couple that were guests at the same hotel. For swimming the woman wore a suit that left only her face, hands and feet bare. However the suit was thin and skin tight and showed off her figure much better than the usual costumes worn by the other women round the pool. Her outfit might have met the letter of the Koran, but definitely not the spirit.