Everytime a post gets displayed on a screen, it got transferred over a dozen routers, parsed by a network card, decoded byte by byte to get each pixel’s color and then displayed on screen
Transferring and decoding all that extra data on millions of computers isn’t free
When you make an instagram post that gets seen by millions of people it’s absolutely not negligible to use webp vs a jpg and choosing one over the other because you’re just… used to the extension? is downright getting unacceptable if you are at least a lil tech savvy
People need to start using newer file format for real now. It’s been 20 years