Well, the purpose of Reddit's r/all algorithm isn't to implement some nebulous sense of "fairness" or "content-blind consistent treatment", it's to provide a "good" mix of content from all of Reddit for the enjoyment of users. If one subreddit is swamping the r/all algorithm, it makes sense to tweak it to lower their impact.

Especially if it's polarizing content that might drive a significant volume of traffic that didn't sign up for that content away.