Its like the game theory explored in "A Beautiful Mind".
If you are 4 guys all competing for the same girl, you are all mutually excluding each other from achieving that goal. Better to compete for a secondary goal where there is less mutual competition. When you are simultaneously queuing for all 4 game modes, you are simulataneously reducing yours, and others, chances of getting into any single one of them.
Ironically, Nash's doctorate was on "non-cooperative games" theory!
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TLDR: Concentrate your search on a narrower focus, and you improve your success of reaching it, because you have less competition to achieve it (since your participation is mutually exclusive with others).
Should it keep you in 4v4? Or dump you into 1v1?
If it does that, what happens to the 7 other people still waiting for that 4v4 you just got dumped out of? They end up waiting for another player, in the interim of which possibly another player gets dumped into a 2v2. Ergo ad nauseum.