I'm also not very well versed in what you mean about Steam; are there specific types of games that Visa and MasterCard have prevented them from selling recently? I've used that service for a number of years now, and usually the only titles I don't see on there are ones that have some kind of exclusivity deal either with a gaming console, or with Epic or whatever. I know that they had some controversy a while back over the game "Hatred".
I have also been a little grossed out at the amount of Hentai-like content they've started to allow on their platform, but once I turned on the "Hide adult-content" setting, and setup a few additional filters, it's been pretty painless for me. Is there other types of games that they want to sell, but have been prevented from selling?