Possible reasons why this happens:
- An update was recently released that changed the game for the worse, causing long-time players to change their review.
- It's an early access title that's been abandoned by the developer, and is being justifiably review bombed as a result.
- It was recently included in a bundle, so there's a lot of new players who weren't interested enough to buy the game on its own, but played it after receiving it in the bundle and were unimpressed. I'd give this one the least weight, because often times those are players who just don't like the genre or went in with too-high expectations for a low budget game.