[2021] P2P Lobby is Worthless for Matchmaking

It functions the way it does now because that is what the majority of players and testers requested. There were a lot of requests to make multiplayer the default.
So when TFP got rid of the separate SP/MP instances of the client, it became just one MP instance with the option for Single Player.

And an interesting fact. Originally the game was only planned to be single-player. Multiplayer feature was added in because it was so heavily requested. Which then led to dedicated server code being developed.