Certainly, the slick presentation is a big part of it – that's what you get when 50% of your game's two-person development team is a really good graphic artist. It's also pressing a lot of specific buttons, though.
On the mechanical side, it's within spitting distance of being tabletop Legend of Zelda, which is something that hasn't had a really good tabletop adaptation that actually cares about the particulars of the Zeldalike gameplay loop. (Not that it hasn't been tried – Fellowship makes a good effort, off the top of my head, but its approach to the source material is a little too esoteric for the average group.) The timing of the campaign doesn't hurt there, either, being in its final week just as the release of Tears of the Kingdom is stoking renewed interest in doing Zelda-style campaigns at the tabletop.
On the aesthetic side, it's really hitting that 1990s/early 2000s anime nostalgia that's been badly under-served in tabletop gaming ever since Guardians of Order self-destructed, while sprinkling in just enough influence from modern YA animation to capture the interest of folks who aren't drawn to nostalgia bait. A lot of contemporary games that draw inspiration from contemporary YA animation seem to feel the need to prove that they're Not Just For Kids™ by, like, saying "fuck" a lot and such, to the extent that just playing that kind of source material 100% straight like Break!! does feels mildly unconventional.
Of course, apart from all that, there's the fact that it's been in public development for a solid decade, which has given it a great deal of lead time in terms of building word of mouth – that's a big part of it, too!