I think there are quite a few reason. First the game is pretty good, has a lot of content and there's a clear promise for more. Second there are certainly DC's streams, where everybody can talk to him, can see how it goes, will get a "dose of SS" even if there's no update, may even be able to influence the game and get his tiny bit of content, etc. - that's going to make people spend a bit of money, simply because they like him and it's going to make people forgive if something isn't as good as expected or lasts a bit longer.
Last but not least one can say that DC has a ton of 1$ patreons who often don't really care that much about that money anyway and get access to his stream archive in return. Next to that there are actual rewards you get for pledging 5$ where you get access to the archive, tracker and the possibility to vote. So I'd guess that the 1$ and 5$ tier are the key to his success in this case, especially since people are a lot more generous and patient to when it's about rather small sums of money.
Last but not least his #4 position on patreon in general and #1 within the NSFW games department will have an impact as well. Many people know the game, recommend it, people much more likely to stumble accross it by accident, etc. - that's going to compensate quite a bit and will bring new patreons.
Other devs who actually "sell" their game (i.E. you pledge and only those who pledge get to download the game, the higher the pledge, the earlier you'll get it), depend more on high tier patreons and are under a lot more pressure to actually release something.