It's created and backed by Google, so that's no doubt Jamie's main beef.
Also, when it first came out, most OSs didn't have native support, so saving a webp locally, you could only open it via a browser, or you installed a non native image viewer, not unlike jpegs and gifs during Windows 95
Side note, I personally use nomacs as my default image viewer in Win10 - https://nomacs.org/
I don't disagree with him in many aspects but I also think he's a hypocrite in many aspects so...It just led me to stop caring about whatever he does/says