They can go in the inspector and see “oh wow so many MBs of JS”, but they can’t see the backend.

There is a good point to that: this data that is downloaded is an end user resource. Over a mobile network etc it’ll matter. But the days where it mattered at home/office are long, long gone, at least for the audience of the websites that adopt this strategy.

The obsession I believe is a remnant of these old days. There was a transitionary period still a decade ago (when hn was already not that young) where users would spend time loading a website, then complain about the amount of js on the page and how that is unnecessary. The connections got upgraded but nothing strikes down a habit…