There was a time when JVM ran in the browsers.
That said, GWT was ahead of its time in a lot of ways, but it had warts galore.
I actually enjoyed using them to get around a few browser limitations around the mid-to-late 00s, and they seemed feature/performance competitive with Flash unless what you were doing fit the media authoring model closely. But by then people were skeptical about Java and if you had to do anything to get it installed they wouldn't, and the direction was native web.
That web application is still in use, in production, today.