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OK. I think I get it. So people enable uPnP on their routers and then open Minecraft’s port using uTorrent (or any other program that opens a port with uPnP). And they do all of that instead of just logging into their NAT routers. Honestly, sounds like something I would do before I knew networking concepts, though if it were explained to me it would be a million times more confusing than just learning how to configure NAT.
For purely political reasons. These users will join and then forget about it after a week because the platforms are different.