The problem can't be the NSFW content, in that case just ban all that content and that's it.
The problem is not the rev share either, if you are looking to earn money, you force a minimum rev share to be placed instead of removing those people from your payment system.
The problem comes from violating the TOS of one of the companies that are used to pay/charge for the games. Here we can only guess what really happened, some mother who complained in paypal for what her son bought. A letter from paypal to itch. A consultant who alerted itch to a possible danger, etc.
The point is that any paid game that uses paypal, strep, etc. and violates their TOS, jeopardizes the relationship between Itch and that company, which is why Itch is separating them from their pay-per-collection system.
Itch has always been characterized by being reactive and is made up of a very small staff for the amount of content it handles (it's easy to find games that violate copyrights, for example). Possibly it is very difficult to apply this rule to all the games that exist (or maybe they simply do not want to?), surely they will try to protect many developers, but unfortunately there are games and developers that it is impossible.
If it's a low-profile game, you're probably fine, even if you don't follow paypal's TOS.
Games that attract too much attention, regardless of their rev-share percentage, will be a danger and therefore, they will be removed from the payment system.
The games that are in between, will be more difficult to classify, but for example, if you share part of your profits (more than 10% for example) you imply that you support Itch and its community and that makes you gain sympathy from the staff and they may try to be more lenient.
On the contrary, if you earn hundreds of dollars a month, with a rev-share of 0%, you will be perceived as someone who is not interested in being part of the community and therefore, the staff will have no problem applying strictly. the rules.
In conclusion, if you want to play safe, you must abide by the rules of paypal and the other companies (that means no more NSFW games that use the Itch payment system), if you don't, it is possible (not 100% sure) that you will end up receiving the email if your game attracts attention.
DISCLAIM: I don't work or know the itch staff, this is just an analysis based on what I've read these days about it.