Because that’s the only reason man, they allow it because it makes them more money. Anyone that disagrees is just silly, how can purchasing more than one copy of the game not make them more money.
In addition to all the posts made, I think one should not justify for thinking the same way as you do. Because one thing that is without doubt a very serious side effect of smurfs is the motivation of players.
The amount of “lower ranked” players quitting or potentially quitting this game eventually will rise because at some point or day when you queued up against 4-5 smurfs, people are fed up.
And it is not gonna cut it to tell those players to “get gud” they simply switch the game and that’s that.