How did I forget about Aurelia?? Agree.
Aurelia is so good, because it's well done and pretty uniqe. Though it is probably true, that many people struggle to find pixel art really erotic (at least that's how it's for me).
That kinda highlights this whole problem. People won't, as far as I see it, easily spend a lot of money on games which feature anime-like art (because there are just sooooooo many of them, everybody has played like 50+ and because that stuff is just everywhere), on RPGM-games (because most of them feel the same and they almost always feel dated) and on games which feature art that's too simple. Once you exclude these factors, there's honestly little left. If you then exclude some niche'ish concepts (like some themed trainer games) the alternatives become even fewer. Sure, there are some notable exceptions, but really not that many.
These last pages summerize that problem quite well. There aren't many actual 2D alternatives to SS around in the western market and as long as that's the case, games like SS and WaL! will still do very well.
There are many great and at times quite uniqe games in development (like just off the top of my head House Chores/Siren's games in general, Demon Deals, Night Driver, Quickie or Aurelia) and I'm happy to even pledge to some of them, but if you look at it objectively, they simply don't have the potential of SS to make money with the general public.