I'll be honest and say I think this is a mindset that dommes have forced on punters as they can't be bothered to offer a full service. If you go to someone decent , say red haired cutie or lndon retreat.. You can get the full on BDSM service and a full service too
No, that's not right. Guys who are into the submissive scene don't necessarily want sex. I'm sometimes in that mood myself; I don't deny that there are crap "mistresses" who take the piss but there are also real experts who perform the role perfectly and give submissive kinky punters exactly what they want.
If you're into that scene it is very different from regular punting and it genuinely is not about sex although it is very erotic at the same time.
Not everyone's cup of tea, as I said, but I can assure you from personal experience that it works for some.