Exactly why this is still a problem. There are patents of game mechanics that prevented other devs to implement them, because they do not want to go to court or fear they could lose in a court. The Nemesis system is such an example often brought up in discussions like these. Or the ability to catch a Pokemon with the Pokeball in the way Nintendo does, and riding/flying with a monster are also patented. And on that note, I think Nintendo lost the case with the riding or with the catch mechanic, I don’t remember details.

Game mechanics being patented is enforceable as far as I know, but only if the patent is in that country and is valid (validity can change even after it was granted, but that is not common). The point is, if valid or not, most companies just stop using those game mechanics out of fear. And that still holding back innovation.