They even addressed the reasoning:
They also noted why they think this is good
But we don’t know what that exactly means. What are those “unwanted effects or trends”? Who do they harm? Who would suffer from them?
Anyways. They wanted to avoid a huge discrepancy between shuffle and 3s would be my guess. 3k in shuffle but 2200 in 3s would look weird they thought and it would kill 3s even further, because no achievement hunter would queue in the harder bracket.
The overkill was simply the MMR reset in Shuffle this expansion with the drastically nerfed mmr gain in its extreme (top rated players). It wasn’t great in DF, but you were at least able to do your Legend wins and stuff. But right now, even that is impossible because the system doesn’t really allow you to climb.