Also GWT apps were pretty slow to load and start, and were very "app"-like as opposed to web-page like at a time when that was not as familiar as it is today. That's how I remember it anyway. And pretty heavy, developer wise, at a time when "update a file on the FTP" was still normal.
It actually worked decently well, but was due to Java needlessly verbose.
WASM lets us run other languages efficiently in the browser but that just opens the field to a lot of languages, not one language to rule them all.