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.
partly, i don’t think it was just that. mng did have considerable benefits over apng at the time; but it was a solution looking for a problem. i think they wanted it to succeed because they’d poured time into it, but nobody wanted to support it (mozilla, the only browser to support it to my knowledge, dropped support eventually because the mng decoder was bigger than every other image decoder in firefox put together)