If it was so simple, why do all the porn devs stay on Patreon?
At least for many people, the ability to use Paypal is a great plus for Patreon.
because patreon is a site everyone knows and trusts (since is pretty much the first one) subscriberstar not so much, its known here well because we all talk about through the forums and etc but to the "average" person its just about it being on steam or patreon they don't really know the other sites or trust them, so devs stick with patreon cause its 100% the better option to attract subs, but we are taking about a game that already has name for itself so its no longer in the "attract members" stage its just getting some to transfer over, and if a dev they trust (surely they have to trust him a bit if they're shilling out $40+ a month to him) informs his subs its the only way moving forward and to trust the site a good chunk will follow
As to my point about pateon be well known and being the first which is why its used more as an example years ago when FB first came into the mix people didn't trust it either for awhile and we all stuck with MySpace for a good while until word of mouth of FB starts to get good and more people tranfered then we all switch over same with MSN vs Skype, as humans we tend to stick with what we know and generaly try to avoid change into the "unknown" so to speak
so generally speaking it would just take a chunk of devs to switch over and the crowd will follow naturally since us human are a herd animal after all.
edit: forget to mention the general stigma of actually supporting porn, saying you sub on patreon could literally mean you're subbed to anything but when the charge says "Subscriberstar Adult" there is no doubt of what you're paying for/supporting seem silly people would care but alot of people do for some reason (but i admit thats probably just a minor thing) So its more socially acceptable to be subbed on patreon then subscriberstar. (public image, patreon all audiences, subscriberstar geared towards Adult audiences) Might as well announce you have a paid prnhub account (which majority of people wouldn't admit despite everyone using porn hub Lol)