Maybe that's what NTR devs be tryna do when they add happy routes to their games. Elevate both in one experience. It's a shame they usually end up being super boring or meh.
Jack of all trades, master of nothing. And the reason they do it in the first place is likely not the one you mention, but the aim to rope in more people into giving them money.
Then they'd threw in few lines and pics/scenes once in a while, no clear end in sight, just to milk people. So it then either gets abandoned after some time, or gets finished in some 5-10 years, or maybe the process starts all over again with labelling a game sort of remake/remaster... Well, guess porn addicts are just like any others. Just wanting to get their money to their dealer, letting the whole system exist and prosper.
E.g. look at The Adventurous Couple. There was a remake, there are some frigging 'seasons' now LMFAO, but you look at the changelog. It says:
- 3500+ lines of script
- 450+ new renders
- 18 new animations
What does such metric tell you about the dev's thinking, their goals? Or the overall state of the game or its purpose? There are no updates to certain characters arcs' mentioned, no updates to routes like cheating or sharing, no mention of some endings, God forbid, or some of them being ready or almost ready. Just the mention of quantifiable amount of slop that has been produced since the last update, with the simpliest thought of doing the same over the next month or few till the next update arrives, to keep milking the patrons, preferrably indefinitely.
So yeah apart from this little rant it's probably best to mix and match it yourself, playing some impactful NTR games and then throwing in the mix some good netori/vanilla ones.