Just like with any other media, popular and good aren't always the same, despite there being a fairly close relationship between the two.
The reason for why critical acclaim is a better measure of whether a book is good than popularity is because critical acclaim is explicitly and directly concerned with assessing the quality of the product. As opposed to popularity, which has zero explicit relationship to the quality, it is only concerned with the raw demand numbers.
Just because mcdonalds is one of the most popular (if not the most popular) restaurants in the world, it doesn't mean that the quality of food there is better than that at a random much less popular Michelin star restaurant.
In the same vein, Transformer movie series is of a pretty terrible quality, but it is insanely more popular than something very critically acclaimed like Parasite. Just looked up numbers, and the first Transformers movie alone (from 2007) had about $700mil in worldwide sales, as opposed to about $250mil for Parasite. And mind you, Parasite wasn't some unknown indie movie that was critically acclaimed. It was one of the most popular critically acclaimed movies out there.