Well i don't take that from just hearing things.. I go to the patreon page of the dev of a game and i always see that games with just romance/corruption/vanilla sex/harem have a LOT more paying patrons then games with what you call NTR.
On the other side i am NOT into NTR by its definition. I have no interest in "stealing" one's woman or having my woman "stolen"! What i want is a western type of "open relationships" and "swinging" with consent and permission and with the consequence that the relationship is improved, not destroyed.
And as an example, as I said, the game that comes the most near to what i have in mind (although it mixes up paths like hell) is The Adventurous Couple. Now if you look to it's patreon site you see 295 patrons on only 4 levels of which $25 is the highest. Not bad.. I've seen worse. But..
Compare that with Mr Dots' 3,262 paying patrons for instance, with 9 levels, the highest being $100.. And he also has only 1 game on Patreon at this time, Sunshine Love, which in fact kinda sux.. but it's of course "harem" and .."no NTR"
Not to mention Dr. PinkCake's 9,100 patrons on 10 levels with the highest being $150! All for 1 game: BaDIK. Coz his first game is completed since a long time. Now truth must be said: BaDIK is really absolute TOP! From almost all points of view. But again : romance/harem/college/ yes, even some cheating but not from the main girl (if any lol) and NO NTR by it's definition! Also not by my definition which would be "open relationship"..
You can look also at the patreon pages of other games related to or including "sharing" or an "open relationship". The good ones among them hardly reaach 100-200 paying patrons. Only those with "cheating" may go a little higher, like Anna EA with 960 patrons on 5 levels (max $25). But cheating is not really my thing. I want it consensual. And that's not interesting for the majority of players.. see what i mean?