Mozilla didn't support WebP for years. I'm fairly certain one of the official reasons they gave for not doing it was that it wasn't a massive jump in quality over JPEG, which obviously would have been good for the web if it was true and motivation for them to support it sooner than they did.

Notably, when they did add it, Edge did so around the same time, which seems to me suggests some politics in the background, (not in a conspiracy sense, just an agreement based on interperability) which I suspect might apply this time too.