The incentive should be people like me, i.e. people who do not participate in Patreon model, and buy the game only on releases on Steam.
If his dev time stretches on even more, rational consumer behaviour theory dictates that more people to switch to my model, rather than Patron model.
I'm not too familiar with Steam but don't you have to wait for an entire season to be completed before being able to get it on Steam? That seems like the wait would be even more tedious.
If Icstor could maintain his Patreon base for years while doing nothing, DPC who consistently delivers high quality and high quantity releases shouldn't have any problem.
Many of his Patreon's are probably on the $1 tier all year round and just go to the $5 tier each time an update is released. That's $20 a year for two very substantial releases (or $10 per episode).
Is it worth it? That's up to them. But $20 a year isn't going to break most people's bank.
It's obviously cheaper buying it from Steam, at $14 a season ($3.50 an episode), but then you have to wait 2 years between releases instead of 6 months.
DPC is very driven, but he's also very rigid. He picks up on some minor suggestions, but he's not about to change how he operates when he's pulling in, at a bare minimum, $270K a year (assuming every single Patron is opting for the cheapest option - which they aren't, and discounting any Steam sales - he's surely clearing $300K).
So no, he doesn't have any incentive to compromise what he wants to deliver by reducing content, or hiring others (which would significantly eat into his bottom line).
Plenty of other great games here are taking just as long, or longer, to deliver less. Of course there are others that are releasing more frequently, but it's not even worth comparing the quantity or quality of those releases.
Personally I believe DPC is doing a phenomenal job. I believe he has a vision, and he is consistently delivering on that vision. If he could deliver the exact same product in a shorter time, and it doesn't cost him more money, and it doesn't result in his wife having an affair due to neglect, and it doesn't result in him dying prematurely, I'm sure he would.
But if he has to compromise on the product, or lose revenue, or it results in depravation of family time, or it drives him to an early grave, I'm happy to wait for however long it takes for the next episode and given the consistent rise in his patron count, I think most of his supporters are happy to wait too.