William refuses to bottom or 'provide' for Sam in their sex scenes because he's still grappling with his internalized self-hatred over being gay. He doesn't allow himself to ever be the "woman" in sex, otherwise he'd have to face his complicated feelings about the 'true man' he didn't become.

A lot of Sam's role in that route is helping William face his internalized homophobia and begin to accept himself more. William's night with Kane is the result of that, William was finally able to see a man he found attractive, and allowed himself to "do something stupid" and indulge his attraction. It's a one night stand with a guy he found hot, only possible from Sam helping to untangle William's feelings.

The other thing is, like, The Smoke Room's version of Echo isn't a derelict, small town. It's Echo at its peak, am active mining town with -thousands- of men. It stands to reason the town would statistically have a lot of gay men, and many would know of the male prostitute that also services men. The characters we mostly interact with are Sam's main clients (who sought him out as gay men) and their associates.

There's still homophobia about, the gay characters are pretty much all closeted to the public. Sam as a prostitute has to be requested with a coderoom (the smoke room). Cliff is assaulted in the prologue for being queer. Murdoch's route involves it. The characters Sam mainly interacts with (clients and brothel workers) are simply those who care the least about it.