Any venture into the wildy without the intention of pking (say I just felt like pvming although i regularly pvp) would mean I'm risking my points that I earned through pvp by doing something that ISN'T pvp. People would try to find ways to game the point system, pking their own alts, setting up bots to pk themselves and farm points, etc. Some clans would start requiring people to have a minimum rank/points before they are allowed to join. People would start flaming each other over rankings or jerking themselves off about how much elo they have None of that sounds appealing to me, and I don't think it would fit in osrs. I've seen similar stuff in so many other games with ranked ladders, it gets really old.

If you were to ask me what my favorite pvp was in any game, two immediately come to mind and that's Dark Souls and OSRS. Even though the actual gameplay is vastly different in those two games, both of them have a genuine charm to their pvp. It feels more precarious/spontaneous, the rules are "unspoken", the reward is implicitly useful within the context of the game, and the incentive to participate in the pvp is usually just for fun.

A point system isn't good incentive, nor is it good reward. The people who will care about points will make things less enjoyable for the people who don't care about points but still enjoy pvp.