It's like Bugsnax. It's something that looks absolutely ridiculous from the outside. But then a few people play it and they end up being way more positive about it because they didn't have any expectations and there's a surprisingly solid core to the experience. Then more people play it because the first few liked it, then even more people play it because now it's popular.

That said, the popularity is absolutely a flash in the pan. A lot of people really like the Monster Rancher-style training gameplay, but I can't imagine most streamers will stick with the game when they have to deal with the gacha cycle of waiting for more content and pulling the meta units.