Netori (A male perspective power fantasy), as a genre, has a blend of actual netori fans and the much broader harem enjoyers. And that is the reality of it. By and large, the average harem enjoyer are gonna look for a relatable MC to live out their fantasies. They want to be a good guy, they want to be handsome, they want to be a chad, they want to be loved. So the deviant nature of stealing a happily married woman is rarely the focus. It's usually framed in a way where MC is saving a girl from a shitty marriage or abusive relationship. The MC isn't corrupting anything. It's usually just a harem plot, which makes sense since the harem fanbase is much larger.
In truth, it's this appeal to the harem crowd that prevents netori from really coming to its own. The netori MC should be a complete deviant—basically the NTR antagonist with a massive cock that corrupts women and makes them fall. I mean, that is the fetish, isn't it? You want to play the non-repentant asshole that corrupts and steals the women who is happily married. Look at some of Black Lilith games like Ochiru Hitozuma or Kangoku Senkan. Now that is peak netori.
Those games don't feature much of actual cucking, but your assumption that netori is primarily about the act of fucking a woman in front of their husband or something is wrong. Netori is a mix of male power fantasy and female corruption, whereas netorare is a mix of cuckoldry fantasy and female corruption. In both cases, it's the corruption of the female that is the significant aspect of the existing relationship, not the male that is getting cucked.
But you are certainly correct that whether we take your criteria or mine, netori is still extremely underrepresented. When devs sit down to make netori games, they inevitably end up trying to appealing to the harem crowd (or even romance crowd if it's single LI netori). Basically, they want a good guy MC. And by the end, it actually just is a harem game with minor netori aspects.