What this tells me is that when you build a site that has images uploaded by a user, you do nothing to those images. You just take the upload and stick it in an img tag to display it.
This is the exact problem with developers building for the Web. You'd rather avoid a relatively small amount of additional complexity than build something that's better for users (loads faster, reduces bandwidth, renders quicker).
Even ignoring WebP, you really should be resampling the upload to the right size and running it through something like imagemin to optimize the file size. And there are APIs out there that will do it all for you - it's a post request at most if you don't want to set it up on a server.
