Greatest quality vs sales gaps – and why you think it is?

I was just looking at a couple book lists, one "best of 2024" and one "best-selling of 2024"; it got me thinking more about the gap.

What are your picks for books that show the greatest gap, in either direction (great but terrible sales, awful but great sales), and more interestingly why do you think it's the case?

I've seen plenty on Colleen Hoover (It Ends With Us def on my list, with the movie further boosting sales…) – curious for a broader range, including older/historical works!