And the reason this happens: the queues are combined, so that if you get 1 person in the "Deathmatch" queue and 11 in the "Random" queue, then the game will create a Deathmatch so as to be able to populate it with all 12.
Get this: MANY PEOPLE OUT THERE DO NOT WANT DEATHMATCH ALL THE TIME.
But the way it is currently being done, even if Deathmatch was the LEAST popular of the modes, even if only 10% actually wanted Deathmatch, you would get 70% of Battlegrounds being Deathmatch.
If Deathmatch were the "most popular, but not by much" - say, a reasonable figure like 40%, which might be "more popular than any one of the other modes, but not more popular than all of them put together"... you'd get literally over 99% Deathmatch, which is what is observed to be actually happening.
Please fix your calculations so that the people who want a Random can have a TRULY RANDOM - that is 20% chance of each mode (DM, Domination, Crazy King, Chaosball, Capture Relic)!
(There is another thread on this somewhere, but NOT in the Bug Reports forum, and the way it is currently being handled is clearly a bug - it surely cannot be intended that 99% of BGs are Deathmatch, when it isn't 99% of the actual *players* that are choosing the Deathmatch queue rather than the Random one, but Random choosers are being forced to populate only Deathmatches by being grouped up with people who only want Deathmatch.)