I chose the spread of games pretty precisely, honestly, including CoC/TiTS. (Though I'd imagine CoC being western players' first game might not be as large a percentage as you think. Keep in mind that most people in their 30s were 20+ before CoC existed - I think, it's hard to pin down an exact age for the game's start.) Those factors were part of my overall point (And previous completed games was part of what I meant when I said "prior good will"), that there's a lot more that goes into how much a game gets than "Incest, Harem, 3dcg: profit." There are a bevy of reasons each of the games mentioned earn the amounts they do, along with a fair bit of luck.The thing with TiTS and CoC2 is that they come from the team that made CoC. I don't know about you but first porn game I put any time in was CoC and I honestly believe that is true for the majority of the western audience. Plus both of those games pump out content at a crazy patch (multiple content patches in a month) but most importantly also have very clear niche kinks, namely transformation and futanari. The first excuses them from not having artwork; how could they? And having a niche you serve more than others means that people into that kink are most likely to follow you.
I think far too often people joke (Or seriously suggest) that you can just combine popular fetishes, good 3dcg, and Ren'py and boom, you've got a big-earning game. It's a lot more complex than that. If the devs gave Rowan some serious heat to pack, a mother and sister, and leaned a bit more into harem territory (Which, honestly, this game should already have the harem tag) SoC would not automatically out-earn most of the games listed above. It might not even get all that large of a bump. The equation's a lot more complex than that. Sadly, games don't always get the amount of money their quality "deserves," even when the content "merits" it.
(Also, CoC2 - not sure about TiTS - does have artwork. That's why I said "minimal." They solved the issue you bring up by simply having the art be PoV so the MC isn't shown, something I'm honestly surprised they didn't do sooner. There just isn't that much of it. And TiTS hasn't pushed out large amounts of new content for a while now due to the Javascript rebuild and resulting storm of bugs.)