This is entirely a guess on my part, but I think it's a reasonable assumption.
From what we've seen, I think the payment companies started to put some pressure on Itch to stop supporting adult content. Itch then looked over their adult games market, saw how much money they were making from it, and decided that it wasn't worth trying to hold onto that money compared to the risk of losing the payment companies support for the rest of the website.
Now perhaps some of this is due to revenue sharing issues, and that adult games proportionally didn't assign a good split on revenue... but I think it's most likely that they just don't get much revenue from them at all compared to the SFW stuff and the team didn't think they could fight Paypal or whoever was doing the pressuring on the issue for such little money.
Some people have pointed out that Steam still does adult games stuff, but I counter that with the fact that steam is more than large enough to just laugh in those companies faces if they tried to pressure Valve on the matter. The amount of backlash those payments companies would recieve if Valve was set against them is pretty large, and not worht the risk for them.
Perhaps I'm wrong but this is my take.