Pissing and shitting in mouths is a clearly defined and identified fetish, and easily tagged correctly. The more general term of NTR and it's more specific names and definitions are harder to correctly tag. There's a lot more nuance to defining and identifying such a fetish, and context becomes not just relevant, but necessary. Like all fetishes, it's an acquired taste. What turns on some, may repulse others. Unfortunately, this particular fetish is more difficult to tag correctly. So players may experience fetishes they find repulsive, which is really counter productive to this genre of game.
Nuance is defining murder. You can say you know what murder is, or that all murder is bad, but that's ignoring the nuance of the topic. There's 1st and 2nd degree, voluntary and involuntary, and many more manslaughter definitions. What about abortion, capital punishment, and assisted suicide? Considering, there's even more nuance and context to consider within each of these issues too. Just saying it's all murder, or it's all bad isn't recognizing and appreciating the complexities and intricacies of the topic.
There's also a couple other factors to consider with this particular fetish. Developers can often make certain fetishes avoidable fairly easily with options, etc. Cut out a few images and lines of dialogue, and you'd have no idea the MC just got pissed and/or shit on. It's often a lot more difficult to do this with NTR. Often the fetish is interwoven into the very narrative of the game. So cutting out a few images and some dialogue may remove the overt implications of the fetish, but the act is still implied. Similar to the incest game, and some patches too. Some games ask you to define relationships before the game starts, or the patch changes these names and relationships for you. Often this results in a game that either does or doesn't work narratively depending on if relationships were changed, or patches applied. The game will be nonsense without the patch, or nonsense with the patch, and sometimes neither work because a far more extensive patch is required to alter scenes, dialogue, and the plot enough so both versions of the narrative work in the game.
This relates to another issue. Being a fetish, it's presence won't appeal to all players. Since the fetish is often difficult to remove with options or a patch, some may try to avoid suggesting NTR is in the game and adding the tag. Like most fetishes, it's appeal is often polarizing, or you're indifferent one way or the other. Some may almost require being pissed and shit on to become aroused, others may literally dry heave just seeing such images. Some may say it's not really my thing, but I've had worse Friday nights. For those repulsed by specific fetishes, playing a game then being subjected to them when you weren't forewarned could be upsetting for obvious reasons. I'd suspect fetish tags are often the first thing players look at when they check out a game, and many even set up alerts for specific tags so they know when a game is posted with those fetishes. If a game has a specific fetish, I'd think most developers would want that tag added, since it will attract their targeted audience. Win, win. Everyone gets what they want. Obviously, there may be instances where there's an avoidance to add certain tags to games, because of a fear they'll detract from a larger player base and potential customers. Often though, I suspect it's the nuance of the fetish that causes the issues.
