Make default programs support opening webp files and the problem goes away. Until that happens users have every reason to convert files from a format that is a pain in the ass to open.

They do.

Photos in windows supports it. Preview on Mac OS/photos on iOS supports it. I assume anything android would support it as well. Plus every web browser supports it.

But it took a while for it, and many people are probably running old software without the updates, so at this point the hate has cemented.