They don't know what a megabyte is
The consequences of MBs of JavaScript can be perceived by anyone in terms of performance and mobile data consumption.
+1.
I have been asked by someone in late 40s why uploading a video takes a lot longer than uploading a photo.
They are not dumb people. They just do not know.
The onus is on the engineers to design for them.
They feel the slowness of the page load