It's only common sense, or lack of it, on itch and the payment processors part. Economical theory says that, if there's demand for a product, someone will offer it. Right now there are three of big platforms that allow AVNs (with more or less restrictions): Steam, Patreon, and Subscribestar. So itch renouncing voluntarily to that market, after they stated on Twitter that they would support them, is only giving money to their rivals.
AVNs won't disappear. For most devs, doing this is a passion project that costs us a lot of money. If we are lucky, we can compensate it with monetization, but I guess that less than 5% of devs can make a living out of it. So if we invest our money and our time doing something we love, we won't stop doing it because one platform, like itch, doesn't like it. We will go to the platforms that allow it and work there.
In my case, I decided to continue publishing the game here for free because I didn't want to punish the players who don't want or can't subscribe to Patreon/SS. For this update, I wanted to do an SFW version to be able to monetize it on itch. It hasn't been as well received as I hoped (only 10 purchases when the last time Itch allowed me to monetize the NSFW version I sold 142 games) but I think it's a visibility thing. Most AVN players don't look for games in the general section. I will continue to publish it here (Early access SFW and when it becomes free, the NSFW version) for a couple of updates and see if it's worth the extra work. If not, I will return to publish only the NSFW version.