I think experience is important and people don't realize it because most of the learning people do, happens organically starting in the formative years/up to early 20s.

It's not just about confidence or stigma and it's not about getting your rocks off, it's about having the experience of being in that situation, with everything it implies, adjusting and learning from it.

It's the same with general social interactions, where if you've done little socializing, especially some more intimate/deeper socializing(as in connecting, making friends, stuff that require vulnerability, sharing, keeping up a relationship), you're most likely to be clumsy and stiff at it, not just because of anxiety and the uncomfortable situation you're not used to but also because it's an aptitude you've practiced little.

Every aptitude needs practice to develop and so does this one. Without having ever been in a romantic/sexual situation ,of course you're not going to naturally send off all the right vibes and signals and use body language correctly, etc. By romantic/sexual situation I also don't mean it being a one sided attempt but a situation where there's mutual interest. We all learn everything together and from one another.

Also, I don't see what is so outrageous about the idea that yes, to get a good grip of yourself as a sexual/romantic being, you need to experience being seen as one and you need to be in such a situation where you can express and experience your sexuality with a partner. Knowing your body sexually, accepting your body, knowing you're a sexual person and all that, is not enough because shared sexuality is about more than that and it's a different facet of your own sexuality that comes into play.

The problem is,a majority of the population has at least a modicum of experience by the time they reach their mid 20s. I think people don't realize that even those laughable attempted flirts in school, the awkward hand holding, just going on a date, seeing/feeling someone is interested in you(even if you're not interested in them), all those small things actually do count and every failed relationship counts too, those good times and intimacy you've had while together doesn't go away. Now, most people start roughly at the same time so when they're inexperienced, so is everyone else, more or less. But then, if you reach your late 20s with no experience or very minimal, then the problem is not so much stigma(at least for me stigma is not an issue at all) but the fact that you're unlikely to find someone as inexperienced, everyone is at a different level, with different expectations, they're playing the game on advanced and you're at middle school level. Also, as an adult you catch up slower and the emotional suffering rejection, loneliness, unmet needs cause ,just piles up. When everyone is roughly as inexperienced, that inexperience isn't noticeable, but when most people have a significantly higher level of experience and you're inexperienced...then it sticks out(or you don't manage to stick out).

Thing is, you're not going to get experience(even just sexual) by having a super casual or paid encounter, because the problem isn't not knowing how to get undressed and move your hips, it's forming that connection that leads to it, sending the signals that convey you're sexually/romantically available and interested, allowing yourself to be vulnerable. So I don't think an online hook-up is going to do the trick either

Oh and I think all around it's probably like 5% of people who haven't had sex til their early 30s, 10% at most. It's higher or lower depending on the culture, of course, but all in all.... Sex/romance is probably the most important, predominant instinct/need we have as living creatures, apart from food/water/shelter, it's at the core of our social lives, we're biologically programmed that way for practical reasons. So it's something very common, it's not a luxury, u don't need education for it and most people do just get to it naturally.