Because there is no netori tag lol.
More specifically, netori is marketed towards the harem crowd. As long as they don't show the girl having sex with her loser husband/boyfriend, these people enjoy the power fantasy or "revenge mentality" of getting to be the perpetrator of the ntr they hate so much when subjected to "them." As such, netori is very rarely the focus. It's usually a LI or two that have impotent/asshole husbands that you steal from, justified so that even harem players that are queasy about immorality can feel better about saving the girl from her abusive guy. It's a very safe and inoffensive approach that adds a little bit of thrill to the vanilla harem by introducing an extra layer (kinda like incest being added to typical harem set up). In most cases, there isn't much focus on corruption or the implications of stealing a woman other than the very surface level stuff.
This kind of netori is pretty common, but it's generally not marketed under the "NTR" umbrella, even though netori is technically in that category. NTR fans typically find this kind of story not much different than any other harem game.
However, there are netori games that do appeal to the average netorare fans. Corruption has to be the main theme. In essence, if the MC is truly a netorare antagonist rather than a harem protagonist, a lot of netorare fans will feel right at home. It's basically the same story just with a slightly more focus on the antagonist rather than the cuck perspective, with the female corruption arc preserved. As expected, we only really see this kind of netori from Japanese devs. Black Lilith stands out with Prison Battleship, Ochiru Hitozuma, among others in their line up of VNs. BISHOP, Lune, and other studios that do corruption have stuff as well, AFAIK.
In truth, whether it's netorare, netori, or straight forward female protagonist corruption games, there is a large base of netorare fans that are really in it for the female corruption. So why the apparent discrepancy? It seems like there are much more netorare than netori. Because devs try to capture the broader audience.
- While many netorare fans are fine playing corruption based netori, there is still a significant portion that play it more for the cuckiness rather than the female corruption. Might as well capture that group by going with netorare genre rather than netori.
- Conversely, while many harem/power fantasy players might even enjoy playing an asshole (netorare antagonist kind of person) as long as he is the MC, there is a significant group that doesn't feel so good playing such a shithead. So might as well capture the broader harem base by making MC a decent guy and toning down the depravity/corruption/moral degeneration of the stealing. It usually just blends into the harem genre and flies under the radar of "netori."