The thing about Steam is: they're huge. It doesn't really hurt them if they decide to yeet even a few hundred titles into the void. Corporations are like hydras: they can sever one of their heads and still survive, despite the backlash they get for what they've done.
There are well over fifty payment processors out there, including Dwolla, that Itch could use, rather than going through PayPal, PaySafe and Stripe. (Visa, Mastercard, AMEX and Discover are different entities.) Many payment processors like them utilize direct bank-to-bank transfers. There are payment processors out there that accept adult content-- and they are not shifty, nor are they cryptocurrency (which is an extremely bad idea to use in the first place.)
Nope, I do not think they would have given anyone a heads' up, if they could have. Many companies have pulled fast-and-dirty changes in the past and they will continue to do so in the future (Companies as a whole will continue to make fast-and-dirty changes with little to no notification. It's what they seem to do more often than not.)
Other people have made it known that this has been going on since at least April. Two months is more than enough time to let everyone know that shit was about to roll downhill.'
They could have easily posted ways that developers and game purchasers could take action. They could have made their own petitions. They could have posted advance warnings. There are many things they should have (and could have) done.
Until and unless Itch makes a statement that they have been fighting back, have been attempting to fight back, or are trying to mount a defense against what's going on, I am firmly of the belief that they are no more innocent of wrongdoing than their overlords and the pile of shit censorship group.