I think it’s more like “why are they bothering?” Like, usually for these kinds of single-player games, the reviews improve over time because once the nature of the game is well known, new prospective buyers are more likely to be correct about whether they’ll like it or not, so new reviews are mostly from people who self-selected for being likely to enjoy the game.

So either people are getting worse at knowing if they’ll like Starfield before they buy it, or they’re buying it despite knowing they probably won’t like it so they can leave a negative review, or people who bought it at release are going back and reviewing it months later.