I simply cannot grasp why someone would not play a game to avoid a rules-set. The rules is not the game. The rules is not the fun. The fun is to meet with friends who share a common interest and roll dice.
There can be a lot of reasons. A big one is time.
Most of the gamers in my 2 active groups are married with children. They don't have a lot of time to game, so when we can gather, they want to
play. Their interest in learning something new is almost nil.
Another reason is genre. Some people I know only like High Fantasy RPGs and have no interest in Sci-fi, Horror, Modern Fantasy and so forth. Some are even more limited, only liking a particular game within a genre.
Each genre has its preconceptions, and they get codified into the ruleset. If you don't like the preconceptions, you're not going to have fun playing any game in the ruleset. Consider Vancian spellcasting, which some (not me) consider the bane of enjoyable fantasy roleplaying- if you honestly hate Vancian casting, you probably avoid games with it like the plague.
Personally? I'll play just about anything. My taste in games I'd
run is much more limited, of course.