In summery this... NTR demands a nonsensical story to work.
IRL hardly any NTR storyline would work.
IRL: Boss fucks your wife and you catch them? --> Wouldn't end well for them.
NTR: Boss fucks your wife and you catch them? --> Oh no, there is nothing I can do... and/or OMG why is my small peepee getting so hard...
You have to dial the suspension of disbelieve to over 99999999999999.
Sort of in RL the odds of this coming about are very small. It requires so many things going wrong that the odds of it happening are very small. That said there are 7 billion people on earth so maybe 0.001 % of them or less might find them in such a position.
That said it isn't that hard to come up with scenarios in which it could happen. Those that can't have no real understanding of what it takes or no imagination. Which is probably why so many resort to trying to use blackmail and other cheap methods to create the scenario or worse try to make the person ok with it or even like it or even beyond that.
The other aspect is that no situation is going to lead to a person permanently accepting the fate of real NTR. They are going to rebel against it at some point even the person with the weakest constitution on earth is going to become hardened from enduring it and lash out eventually or try and simply escape in whatever manor that is.
We could break it down into components. You need a situation in which the person can't easily leave. It helps if they have something they want to protect to keep them there.
The situation can be created in a number of ways. It could be physical limitations, economical, it could be cultural, legal, ...
Examples:
1. Consequences of past criminal life. Such as in my prior post. Doesn't even need to be criminal necessarily just bad choices or choices not accepted by others.
2. They could be a lower ranking member of a vampire coven, that can give you multiple reasons why they don't rebel. They would need to survive on their own, if they take action against those who are doing it it could lead to having a lot more powerful beings pissed off at you...
3. They could be serf in the middle ages, they can't simply get up and leave. If they do the entire family can be punished for their actions, they can't take actions openly for the same reason...
4. They are stuck on an island, or any other area that is isolated and hard to leave. If you were at an oasis surrounded by desert to large to walk across it would be as effective. Especially if here was no other means of transportation other than walking.
5. If you are in a walled city surrounded by monsters ...
6. If you are in a state such as that in the book of 1984 were you are continually monitored again it would be hard to do anything.
7. You could be a member of a criminal organization that keeps tight control on the members. Or any other organization that needs secrecy and security to a large extent be it military, spy, some corporation that trades stocks and uses illegal means to get info to hold the upper hand...
This list can be expanded a lot.
Something to protect:
Their own life, family, children, wealth, a business of the family, ancestral land... Hell it could be pretty much anything if there is some sort of value placed on it.
Those are fairly loose listings above. You could define each of those much more and should in writing a story.
Considering I came up with the primary basis for that many means of creating the situation it shows the people writing the current games have put shit for effort into it at all. Most just look at other games and cookie cutter the shit out of what they see others do.
Given that list above. If we take it and add in a detail system for coming up with places, locations, names, ages... and so on. We could write a script that could generate better scenarios than 99% of the current games out there.
None of those above require any form of blackmail to be used. All of them simply rely on the consequences of acting against the situation as a deterrent.