People are already conditioned to need a web browser to view adult content, and if you are an adult content platform, your competitors are also missing from app store as well.

This doesn't work out the same for social media. Doubly so because a social media platform benefits from integrations like notifications which are missing from iOS Safari.

Perhaps. I’ve been using Twitter and FB exclusively via iOS Safari for a year or two and I’m not sure I’m missing anything important

You miss App icon on share sheet. Maybe Web Share Target API solves this situation but I don't know Apple want to implement it.

https://bugs.webkit.org/show_bug.cgi?id=194593

That's like saying PC gamers are conditioned to using windows. They're not "conditioned" to anything, people go where the thing they want is.

And if they want it bad enough they'll start going somewhere new. Which is why most of the synthetic recreational drug crowd learned how to use tor and gets their product delivered in a little bubble wrap envelope that says "agricultural chemicals" on it.