First, our culture still enables men to be crap about sex in general
Our culture still portrays men as the ones with sexual agency. Sex is still about men, and most men themselves approach sexuality in a wide-eyed boyish way that combines innocence with a lack of reflectivity: "Me... me... me..." In this world, female pleasure is a proof of masculinity and the female body territory to be conquered.
The unreflecting assumption is that Femdom will simply be an inversion of traditional male/female roles, hence the obsession with "serving" one's mistress by being penetrated, and hence unsolicited ass picks.
Couple that inversion with sexist assumptions about women's "naturally" subordinate role, and you explain why malesubs are so keen to emphasise their lack of masculine or high dominance traits: "I know you're a mere weak woman, but I'm a total loser with a small dick who likes wearing panties so you will be able to dominate me."
This exaggerated inversion makes sense when the sub is in boyish mode, but not after he's had a good orgasm. Hence the tendency to flip flop, overcommitting then retreating.
Second, Service Femdom is more visible than "Actual" Femdom.
Prodommes are disproportionately represented in mainstream media, and have a disproportionate presence on the Internet. (After all, this is their vocation. They are easy to contact, often look good on screen, have lots of cool gear, and - if articulate - have tonnes of practical experience to share.)
Meanwhile, the Internet is a good place to talk about the technical aspects of BDSM, so there's more online information about cool rope tying techniques than there is about kinky dynamics and emotions. This makes Femdom look like a service, even when it isn't.
So it's easy to regard dominant women as a cheaper alternative to a prodomme - the equivalent of the nymphomaniac of 1970s sex fantasies: all the convenience and lack of complications of a hooker, but free.
(And perhaps there lingers the assumption that women don't really experience desire anyway, so all straight sex is service; why should Femdom be any different?)
Finally, porn amplifies all this.
Not much to say about that one!
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