Matchmaking without custom servers/lobbies makes finding a match even harder, since a minimum amount of users in a specific ranking/skill level/ship tier/whatever must all be online and searching for a match at the same time. Custome servers and lobbies allow just one or two players to start, and it advertises to other players that they are available to play. The initial players just need to wait until more people show up, and can play more casual game modes or with bots or whatever until more people arrive.