I suspect a lot of people followed it because there are not many well-made NTR games.
In my specific case I actually played it with NTR disabled, purely because I thought (a) the girls were gorgeous and (b) the incest slow-burn was done properly. For taboo to really be taboo, it has to be a little scary to those involved; the MC did a good job of really showing how the girls involved were so reluctant while still being sexy and eager. Overcoming the reluctance (in this case, through drugs and being an asshole) took time and was sexy to observe. If I was a self-insert type I'm not sure I'd have liked the MC very much, but I play as an observer so I found it pretty erotic.
I was also intrigued by the hints that he'd be moving toward my favorite kink, lezcest; the story never quite got there (other than a background shot or two during a basement orgy scene) but it was definitely headed that direction. That particular fetish coupled with slow-burn and reluctance is pretty fucking hot.
My guess is the NTR tag scared off a ton of people. Additionally it was also a buggy mess (events triggering randonly, scenes out of order, etc) and the dev himself was a bit erratic. Basically the only things the game had going for it was (a) pushing some under-served fetish buttons and (b) great art. The writing was mid-tier, but the rest of it was a mess.
Basically, the game never appealed to that many people, but those who did play it were pretty loyal.
Check out the game
Light of My Life for another example of a community being crazy loyal despite some bad developer practices. The girls are not very attractive (deliberately!), the release schedule is insanely slow, and the dev is a bit of an odd duck (putting weird pro-f95 pirate cosplay scenes in middle of the game, for instance). However, it hits an underserved fetish (lezcest) and _really_ nails the slow burn. That is enough to get people (including myself) to keep sending him a few bucks even after 12+ months of no releases.
