Thank you. Most female co-workers aren't capable of providing introductions for the reasons mentioned above.
I have changed employers numerous times over the years. I've been able to see this phenomenon in multiple organizations.
There are penis carousel riding females in various organizations but I've never had a female co-worker I interacted with regularly who was one of these never married, carousel rider women. Penis carousel rider single women are outnumbered in most workplaces by married women with children and unmarried women in multiple year long LTRs.
It's possible this can happen, but I think it is less common.
If this were to happen, it would be an indicator of the man being too beta and his female co-worker perceiving none of her friends would be interested in him long term. The co-worker can sense that her friends would ditch him after 1-2 sexless dates and she doesn't want to open that can of worms. The female co-worker would never use these terms to describe the situation, but she might think to herself that there's no way her friends would find this man attractive enough as a longer term partner.
If a guy were actually great, she would have no reservations about having him meet her eligible friends.
This doesn't happen much because the typical corporate woman is a married woman living in her married woman bubble. If unmarried, she's also probably in an LTR with all friends in LTRs or married.
There's a good chance the HR rep picked up on your social awkwardness.
She and the hiring manager probably let it slide for the reasons you mentioned. You have a bachelor's degree in a job that doesn't require a bachelor's degree. Your social awkwardness isn't going to get exposed in the role as it is designed in that company.
There's probably a 0 chance that HR rep would have gone on a date with you if she were available and attractive 6 years ago when you initially interviewed.
In companies that are very STEM oriented, there are female HR reps who are neurotypical interviewing men with a good chance of being autistic. These neurotypical females have to figure out which socially awkward men are worth presenting to the hiring manager. In many cases, the hiring manager is an autist too.
Off the top of my head, I can think of 2 carousel riders I've worked with through the years, one of which threw choosing signals at me (but my phobia of risking a rejection from a coworker, combined with the fact I have hardly any experience pursuing cooch outside of tech methods, stopped me from acting on her choosing signals)
It's possible I've unknowingly worked with some more carousel riders (as carousel-riding is the type of thing a lot of carousel riders would hide from coworkers)
The fact my jobs tend to be less professional could explain why I (from the sounds of it) have worked with more carousel riders than you have.
You're probably right when you say it's less common for female coworkers to refuse to introduce a single male coworker to single female friends solely because the female coworker thinks her single female friends would quickly lose interest in the dude, although that's probably been the case with me to some degree through the years. I'm an outlier in many ways (and if a female coworker discusses the topic of relationships with me, it will come out that I have a hard time keeping a woman, which is probably a red flag to the female coworker)
Interesting thing about the HR rep who interviewed me, one time (after I had gotten settled into the job) when I ran into her, I commented that we hardly ever run into each other (as we worked on different floors, even though in the same company). She replied "If you want to see more of me, my office is upstairs." I initially interpreted her comment as a possible choosing signal. I then found out she made the same comment to another guy in the company. She's probably just a tease.
That HR rep, no longer with the company anymore, is a year older than me, attractive, and I never heard anything either way about her relationship status.
