I don't think that's peoples problem at all. With an already established series such as SAO and the fleshed out characters, the theme of NTR just doesn't fit the characters whether the NTR theme is Netorare, Netorase, or Netori. In SAO cannon universe, Kirito is a hapless carefree Harem of Friends plus one girlfriend Protagonist and the rest are just stuck in the friend zone, the reason for that is Kirito has no real competitive antagonist as he defeated all his enemies, but the primary problem of that is that there was never any real rival for Kirito to compete with -- and so, NTR Game Devs have to create one, whether people like that fan-made character or not is left to their own devices.
I plan on creating one as well, but before I create the SAO NTR game I intend to create a fan-made RPGM SAO game that is as close to cannon as possible, and give Kirito a rival. It won't be cannon as I'm not the creator of SAO so nothing like that, but, my game is gonna be at least within the cannon universe of SAO and it won't be a hentai game. It's just going to establish other characters so it doesn't just look like Kirito is the only heroic protagonist, he's at least going to have a rivalry with another character or multiple characters that can do more than just compete with him in games. Hopefully this will help flesh out the antagonist characters in the SAO NTR games that I do intend to make afterward.
Doing this my hope is that maybe players of the SAO NTR game I make won't find it so jarring when Kirito is faced with a situation where he could lose his girlfriend or harem of closest female friends, and I won't have to completely break their cannon character personalities.