FUSE is generally shipped as a separate executable, which requires no modifications.

So no, GPL would have changed nothing. Companies would still have been able to ship it unmodified for free without contributing anything.

They could have kept their own code that uses FUSE secret, but even if they had had to release that code, that code is often useless to anyone else. It would not have helped or supported the author of the original code in any way whatsoever.