I think it's a mix of
- new people, and certain long-time lurkers posting more (for the poll or otherwise)
- lots of new series all at once
- more focus on sales and rankings outside of the magazine recently (everything seems to start low making it hard to tell what'll do well from ToC alone)
- and what I feel like may secretly be the #1 thing, the death of very early leaks from MS and jimbox
Now we've essentially got more people and they're all reading the new chapters at the same time, since viz/manga+ is the best option and has a specific time they're released at. In addition to that, since viz translates all WSJ series (except Yuuna), many are probably reading more series from jump than ever before, since if you're going on to read kimetsu/black clover/mha/one piece you might as well check out that new manga that's conveniently right there next to it.
Mitama's a great example of that, probably only 3-4 people would be reading it here if it came out a couple years ago (since gag manga never get scans), but instead it's actually decently well liked within the topic.