Klepar The thing people like about them is that it lets you live life as a game, unlike VR novels which tell you its a game, the game element genre with systems is the ultimate fantasy of fantasies. If you want to say it crudely then it's just the best wish fulfillment and the most fun way to imagine life being in a world you transmigrate too and if you want to say it politely.... Well I can't find a way to say it politely. But seriously, when I read I become the MC, I compare the MCs actions with what I would do or at the very least I compare it with what I would like to think I would do in said situation, that is why I can't read most female protagonists novels, because I could never imagine being reborn into a girl and suddenly liking men, especially the jackass rapists most of those men are in those stories. Do you get where I am coming from with this? It is the same reason why a trash manhua like The Gamer is so popular, the plot sucks, the characters are lame (except the loli, because loli=greatness), and the only thing that makes it good is that an average smuck like you or me suddenly picks up game like powers and lives life like a game, without the adversity obtaining that strength normally would entail. The biggest selling point about game elements as a wish fulfillment story is that literally any system could be used by anybody in most cases, afterall as long as one is willing to grind and put in the effort they can stand above others, unlike reality where even if you put in 10,000 times the effort of other people you can easily still fail. Even if these novels never become your favorite, they are always enjoyable, as long as the novel is even slightly decent it will still be something you enjoy reading.
Okay that got a bit long and I kept repeating the same premise, but I think that should be enough to explain 99% of the reason people like system novels, as for the other reasons? Honestly I don't know, I mean most system novels are funny and give the excuse to OP the MC in some way or another, and people love OP MCs as well, so maybe that is why they are so well received. As far as I'm concerned if I could get a cheat I would choose The Strongest System or The Ultimate Scheming System 10/10 times......................... Maybe, I mean I'd also be willing to take the QQ farm cheat, that thing is awesome and is pretty much 2/3 of a system in and of itself.
Don't forget some trash system novels, like Plunder the Dao of the Immortal Journey or Invincible Level Up. As I've said, they aren't all good, but the ones that okay automatically get treated well, but the ones that are trash are usually uber hated, and I mean so hated they forced an old man like me to use the word uber.