Kimetsu stands out because people are posting and focusing on the sales info every week. Nobody really does that usually.
Also because it was pretty comparable to Black Clover before in popularity and sales so a lot of us were expecting a similar sized boost, where it'd grow a bit but stay as a mid-magazine series rather than catapulting to being a front runner.
Speaking of being a new front-runner WSJ is in an odd situation right now where they've essentially got a Big 5 face series. OP is #1 as ever, MHA is the clear #2, but Haikyuu's dropped while Neverland and Kimetsu have grown to the point that the 3 are all pretty much at the same level.
and then there's the all the flops at the bottom too giving the magazine a weird balance.
top - OP, MHA, Haikyuu, Neverland, Kimetsu
mid - Black Clover, Dr Stone, WNL, Yuuna
new-ish and growing - Act-age, Jujutsu, Chainsawman
new flops - Yui, Beast, Shinobi, Taisei, Samurai 8?
it's pretty even at each tier, granted OP is really it's own lever and Black Clover is I think a little bigger than the other mids but still.