I'll by the lazy developer / uninformed business owner explanation or the flash cancer analogy, but the tracking explanation seems a little far-fetched.

I get that Facebook, Amazon, Apple, and Google are all running ad networks trying to track me, and that globally this accounts for most of the bloat.

I'm trying to understand the dynamic that causes what should be simple static websites to use JS in such a way that they display no information at all when JS is off.