1) The main point is that a 6/10 game probably does not belong on a "worst of 2020" list. Especially if there wasn't any hype behind it that may have lead to some massive disappointment or whatever, it feels cruel to add a possibly underwhelming, but otherwise decent indie to a "worst of" list.
2) As for why people play "6/10" games, well... perhaps it's not a 6 to others? If it's in a genre or style that someone really enjoys, or if there's a uniquely appealing aspect to the game amidst its flaws, what's an unremarkable game to some might be more enjoyable than a popular "9/10" game because of the niche appeal. I'd rather play a 6/10 Souls-like myself than the newest Mario game, simply because I enjoy those types of games more. My time is enjoyed more when spent on that then on a so-called 9/10 game in a style I don't care for. Frankly, your comment about "selling themselves short" feels kind of condescending. I know what my time is best spent on, thanks.
That said I only played the Hellpoint standalone demo and not the full game, but if it's representative of the final game, I would agree with the consensus in this thread that this game doesn't belong on any kind of "worst" list. It's a competent sci-fi Souls-like, at the very least.