MAU's are completely pointless for game design. If you log in once for...20 seconds....in some calendar month. That counts as 1 MAU.
If you log in 65 times in a calendar month and play for hours every day: That also counts as 1 MAU.
So the idea that grindy game design is some indication of player approval is bullshit. Monthly active users is just that: a count of how many accounts that accessed the game in a month.