I don't understand why people play multiplayer games when they don't wan to play with people.
They don't want to play with people. They want to play against people. This is most clearly seen with scrub accounts that people use when they feel like curbstomping their opponents. The really bad offenders would purposefully tank their scrub accounts' matchmaking rating so that the accounts' rating is artificially lower than their true rating, which means they will almost always be matched with players with a lower rating.