Maybe they upgraded their bodies to be more human-like, in-universe explanations, probably. You're close, Cybertronians may have possibly been given THAT upgrade. Swim trunks? Yeah, I saw 'em. So it seems...
Oh yeah, hey guys, if re-read the comic page before this one, Stone's explanation for why they're wearing swimsuits is seawater affects armor differently from fresh water (it's more corrosive).