Speaking from past experience in offline retail, "best sellers" may at times be items that actually may be a special purchase and a merchant wants to feature or might be a style they hope to sell a bit more of before it's marked down or put in clearance.
Yes, I've noticed the same thing online, seeing best sellers lists with some quirky items. But in all fairness, I've had some of the strangest things sell very well & then see those items listed as best sellers in a merchant's aff newsletter or on their website.
Sometimes, there's no accounting for consumers' taste!
Pay no attention to that woman behind the curtain. -Wizard of Oz