Yeah, more often than not the lack of rules for men's clothing is because culturally, what's thought of as "men's clothing" is so boring that there's no way it could be sexualized.

Seriously here are the bathing suit options for men: Shorts, Smaller Shorts with no pockets (speedo), Cargo Shorts, Shorts with a T-Shirt and (theoretically, I don't even know where you'd buy one) a one-piece. Everything else, mankini or g-string or whatever, is lingerie and is covered under "decency laws" so you don't have to explicitly address it in your summercamp rules (the reason pants arent included in "No Shirt, No Shoes, No Service")

Meanwhile every bathing suit option women have has been sexualized to the moon and back, and half the options are just lingerie that's acceptable to wear in public bcz all our laws were written by horny hypocrites. A men's speedo covers more than your most basic bikini, are way harder to find and aren't usually sold in boy's sizes. A women's one-piece suit is a camel toe nightmare that should qualify as a fucking miracle if it doesn't leave both cheeks hanging out, and now most of them are including a fucking boob window.

We've internalized the masculine aspects of sexism to the point where we don't need to explicitly state it, and instead spend all our time correcting for the obvious cultural deficiencies that result from it and shifting the responsibility for dealing with it to women. "Why would I change my behavior, I'm fine, nobody's ogling me at the pool." It's great. Really winning as a society.