I think you're putting too much stock in the steam reviews. Just because a game has the same % positive rating as another doesn't mean it's of the same quality or even that people like it the same amount.

It's like rotten tomatoes. 2001: A Space Odyssey [0] has 93% on RT, Pick of the Litter has 100%. I'm sure Pick of the Litter is a fine film, but clearly there's a sense in which it's a lesser movie compared to 2001 by general consensus, despite what the percentages would indicate. Now the case of stardew valley and "the other farming simulators on steam" is not so extreme but that's what I'm getting at.

[0] https://www.rottentomatoes.com/m/1000085_2001_a_space_odysse...?

[1] https://www.rottentomatoes.com/m/pick_of_the_litter