"Does this sound preposterous?"
Not preposterous. Just unaware. Not your fault.
Sex is neither easy nor painless for women on the regular. This never seems to occur to dudes... Y'all think that bad sex is when you don't cum, or don't manage to make her cum, or cum too early, or lose your erection - but even then it's usually nice for you up to that point. You might experience actual pain during sex only if she rides you too roughly, or if something outlandish happens with her IUD or her vaginal muscles, or if you fall off the couch and break your peen. For pain to be an aspect of sex for dudes, some accident must occur.
For most normal females, pain and discomfort are the norm at some point during standard vanilla sex - not accidents; just standard practice - and there's room for massive deterioration from there. Depending on hormonal cycles, vaginal dryness, the reckless overenthusiasm of the partner, the size of the equipment, the position... it's about as pleasant as an OBGYN visit and requires about as much prep work.
So no, you wouldn't be doing that casually with strangers all the time, unless you're into pain, soreness, bleeding, and no/unspectacular orgasms for all your trouble. So most women already do "get all the 'action' [they] want or desire", which is not much by male standards, but plenty by the standards of the person whose body gets penetrated.
(It usually just takes one less-than-stellar pegging for males to begin to grasp this, by the way, so... if you really want to imagine it, here's a suggestion...)
Also, as the ladies above have already mentioned, b) sex is nowhere near as fun if there's even a slight chance you can get pregnant, or suffer emotionally or socially from it. Reality sucks, and not in the good way.