I agree with you, but, sadly, long build up stories take a lot of time and money from the publishers and they don't sell anymore.
There is a reason why elf, a very big Japanese developer since the 80s and creator of the NTR masterpiece that is Gatenkei, closed.
You don't see anymore visual novels like Gatenkei, Triangle Blue, Marriage Blue, etc., because they just don't sell nowadays. People don't want to buy things that are story heavy focused. Most of the people just want a scenario with their favorite fetish for a quick fap. They don't want to actually feel bad, be depressed about the protagonist for seeing the most important person of his life being stolen from him.
That's also the reason why the so-called NTR games nowadays are made from the female perspective. In this way, the players see the action quicker than what happened with old NTR games that were from the perpective of the male character. This just loses all the NTR feelings. Those games don't have anything that NTR used to mean. They're all about corruption and they just put a guy there to create a cheating scenario.