Zerg population was at 40% during that time period (at least in masters, diamond). It’s gone down proportionally to protoss in gm. So basically zergs are quitting the game. That’s the long and short of it. There have even been historical spikes where zergs switch to protoss right after a balance patch. Basically zerg is harder and this means players have a worse experience. After getting railroaded with a 5 or 10 game losing streak, they either uninstall or switch races. And that’s how you have zerg’s popularity tank. In particular the low skill brackets are the least likely to pick zerg and that tells you everything you need to know about how difficult zerg is.
So if you want to take into account population parameters to decide how likely Zerg is to generate GMs, I did that once upon a time. I’d have to find the charts. But basically Zerg’s mean ladder mmr is about 100 mmr higher. That means zerg should be the most common in GM, but isn’t.
I actually found it:
https://i.imgur.com/Nhx30S3.png
So population trends predict Zerg is the most common in GM, but it’s the least. Hmm. Why is that.