And it's that way because blizzard decided it's what they would focus on for competitive. If they were holding PvP tournaments for rated battlegrounds instead, that's where the competitive scene would be.
Just because they are doing something doesn't mean they should 1. have started doing it in the first place, and 2. keep doing it.
If the most popular format in the game is 10v10 then the game should be balanced around 10v10, and the competitive scene should be placed there as well.