I grew up in a tourist area where >50% of houses were summer rental income properties. A significant chunk were furnishes with a set of cheap bikes and bike locks for the renters to use. So some significant percent of half of all houses there had 2-6 Walmart bikes.

The guy that has a massive collection of 1930s Scandanavian hunting rifles (or whatever other niche) skews the "average" gun owner stats. I would bet that similar outliers are at play for bikes since it's a similar case of some people use them as tools, a lot of people own a few, some people own a ton