If you see them in browse your account is configured to see them.
The observation that people are more willing to pay for this type of content on average is just this. It is not an indicator for an invasion, but an indicator for popularity.
Speaking of popularity, look at the top 10 in popular sort. That will be 90% horror. Are we invaded by horror then?
And I can even name a reason why people are more willing to pay. Production value and professionalism. If you scrutinize the list of games that have a Steam key, you will find that about 10% of those games are nsfw games, which is a lot higher than the ~2% ratio. This tells me, that on average the production quality of those games is higher. It is not a perfect metric, but it is objective instead of subject. And being able to release on Steam is kinda telling on how professional a group of developers is. Amateurs do not do this. And professionals also do more marketing, like zero cost devlogs.