Not necessarily for being innocent, a bit like my thoughts on pyjamas. More because it is functional and modest. Like the girl in pyjamas is wearing them to be cosy and comfortable, a girl in a Speedo swimsuit or some such is there purely to swim. Last thing on her mind is any thought of showing off, provoking or seducing a man.
Mind you, in this day and age of CCTV cameras, I'm struggling to work a girl out for her swim in to a sexual assault scenario! I got as far as early morning in a public baths then remembered the bloody cameras!
Do pool attendants wear swimming gear under their shorts and t-shirts? I suppose not. If someone in the pool is drowning, you're not going to bother stripping those before you dive in and save them.