And she most certainly will do so, but incest was a tag from the very beginning of the game, and Anya and Maki's interest in the MC has not been hidden. Nor was the fact that the MC would get a lot of attention in general hidden. If you don't like it that's fine, but the clear direction from day one has been that the MC will also be getting a lot. And there's nothing about that which excludes it from NTS. In fact I'd say it's an interesting angle to explore for an MC in a NTS relationship, IRL it's not just cucks that share their GF's, a lot of pornstar/OF couples are open and do all sorts of crazy shit outside the relationship, it'd be hard to argue those guys are stereotypical "cucks".
There still will be all the things you'd expect in an NTS relationship... but again, and I feel like this has been gone over so many times, the pacing is meant to be a gradual slow buildup. It's a porn game but an absurd acceleration into sharing and swinging would not only come across as incredibly unrealistic even within the genre, but ruin the entire anticipation factor.
Most of the people that complain about this seem to be people who don't pay though, given the same complaints are rarely seen on the discord. Curious that.