In 2v2 why does one base end the game?

[Harti]

The team with two players left will gain significant unit advantage within 1-2 turns and simply overrun the other player.

There are situations where your suggestion would come in handy (e.g. when two bases are at stake simultaneously) so one could consider that. 2v2 needs a lot more balancing anyway, from what I found is that if you start a 2v2 game, your position will be assigned randomly and so will the turn order. So if there's gonna be a 2v2 overhaul at some point (not too unlikely), OML could and should consider that.