My impression was the criticisms of flash stemmed from its security issues, it’s closed nature, it’s relative unfamiliarity (compared to popular languages of the time), and the nuisance that was making sure you had the right version running on your machine at any given time. Modern JavaScript addressed these issues, hence its popularity over Flash. This doesn’t endorse the gratuitous application of JS for fundamentally static content, but it sets the context for your perceived “shift in dev culture”.

By definition, everyone agrees that "gratuitous" use of JS is bad. You're glossing over the nuance of the debate which comes down to the specifics of when something is actually gratuitous.