I don't know what a .webp file is but I don't like it. They're like a filthy prank version of the image/gif you're looking for. They make you jump through all these hoops to find the original versions of the files that you can actually do anything with.
Edit: honestly I assumed it had something to do with Google protecting themselves from image piracy shit
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.