Shoehorning formats that were made for 640x480 pictures
Err…nothing in the file format spec restricts jpg to a particular size. I would actually argue that this undermines your point – bandwidth was incredibly limited in the 90s compared to what I see today.
Simple example: a 640x480 image is (at least) 307,200 bytes = 0.3M, so it takes at least 5.4 seconds to transmit over a 56k modem. A 4k image, same color depth, is 16000000 bytes = 15M. On a gigabit connection (what I have), that takes about 0.02 seconds.