Offering a thought I've shared elsewhere:
Growing up in the evangelical-leaning midwest in a certain age bracket, women generally exchanged oral with men very casually. It's not quite fair to say it "didn't count", but it certainly wasn't intercourse and was often a polite gesture at the end of a nice night or something that could be done between friends. For a long time, I thought very little of it, even with attached or married women. (Possibly, some of this had to do with the very intense rhetoric we got about avoiding teen and unwed pregnancy.)
Mrs. E, growing up in a Catholic school, in the northeast, a few years older, got a very different perception, that oral sex was much more intimate and to be reserved. Casual intercourse, also, was shunned, but it usually came first in intimate relationships. Regardless of ethnic background, that was pretty consistent, down to the Puerto Rican girl who would roll her eyes at oral sex but had three or four men in rotation to keep her fucked at any time.
I'm not sure how much of that is cultural/geographic and age-specific, but there are differences there in social groups.
Also, I've known a number of women who disclosed that they had very specific breeding kinks that involved being somewhat anonymously "used" for pregnancy, as well as women who would prefer to have intercourse with someone they didn't really like over oral, and while that's far from universal, I can see the logic of how intercourse is less intimate. Performing oral is usually deeply sensory beyond touch: tastes, smells, often a lot of eye contact. It's full of deliberate choices about how you'll use your lips and tongue to manipulate someone else's body.
I don't think there a clear answers there. As I've gotten older, I've developed a more casual view of intercourse. As Mrs. E has evolved into this, she's developed a more performative and casual view of oral sex.