"This game is bad, according to my preference" means the EXACT same thing as "This game is shit."

No. First of all you are assuming that preference and quality are connected. They aren't for the most part. I prefer Fallouts VATS System over an Ego Shooter playstyle. This has nothing to do with what is "better". None of it is necessarily better. It's just my taste. I prefer open world games, other people prefer a more linear story. None of it is better.

Saying that something IS bad in this context would be completely pointless.

But usually it's hardly ever about constructively talking about personal preferences. It's about people thinking that things ARE bad because they don't appeal to their personal taste while at the same time attacking both those you actually like and enjoy the games as well as the developers.