Because there is some "basic" rules that have to be followed if you want a game to be considered as a good game.
Trying to be different is not automatically a good idea.
Nearly everybody knows that immersion is important for a porngame. Because if it wasn't, then people wouldn't play the game. People who don't care about immersion either just download the gallery or just consume other kind of porn., they don't "play", they "watch".
And since immersion is important, then you need to make sex content more believable which go through context and story telling.
Even games which are not porn focused do that. Sex scenes are not random on Mass Effect, they are all understandable and explained.
No, a game is good because you find it good. And individual taste and preference goes a long way here. I can like games you don't like and the other way around. I like RPG, RTS and similar games, but that doesn't mean I like every RPG game there is, just because its a RPG game.
Some games might have serious issues that make them basically unplayable. Crashes, bugs and so forth. But clunky mechanics and features is something you can work with if you find the rest good.
There is no 10 pt check list a game need to be based on to qualify as a good game.
Trying to copy the success of one game doesn't make the copy any success. Look at all the Battlefield and Call of duty games. You got a few good ones and a lot of steaming turds.
MAJORTY of the games on this site lack immersion. And the ones that try real hard, get thrown shit at for not deliver enough lewd stuff fast enough.
I guess you never watched a porn clip, you need to watch a entire "feature porn" movie with an actual story right? Because you need context?