This is probably because it kinda loses a lot of the 'spirit' of NTR, even Reverse NTR kinda loses its point here because it doesn't feel like the FMC would be 'winning' anything, it's basically just a slut MC who happens to target couples XD
Suguha's plot here works because both here and even in the source material she DOES have feelings for Kirito, and in both she had more or less accepted that he was happy with Asuna and just lived her life fine with that (Granted in the Fujinoverse she never actually made peace with those/got heartbroken like in Canon because Fujino twisted the fuck out of the timeline and made non-stop plot holes to somehow have Sugou's events have happened WITHOUT Sugu's involvement lol), but then thanks to her 'corruption' she just went full-on Yandere and decided to take him for herself. It works so well because there WAS an emotional attachment between the characters before she even 'snapped', so there is several layers of corruption, from Suguha's own love, one-sided as it was, to her actual relationship with her Onii-chan who kept seeing her as his beloved sister and doesn't know she's riding his dick and daydreaming of getting rid of his girlfriend to have him all to herself one day whenever he's online XP
Granted, the 'feeling' is a bit diminished given that she got not-NTR-ed first and also because the girlfriend in question is an unsatisfied slut who prefers the ugly bastard's dick already, but her having gotten free of Hebishima to get here in the first place already makes it very interesting in itself. However in a 'perfect' Reverse NTR scenario, Sugu would just snap or decide to get Kirito by herself one day without needing to be not-stolen first, and Asuna would legit be perfectly in love and loyal to Kirito so the Reverse NTR is actually 'fully realized' (Is kinda like why you won't really see a 'NTR' doujin where the MC is actually just fucking other girls behind his stolen girlfriend's back, because that would make most people feel it never was NTR at all).