It was never meant to be. Just like UNIX initially, it was a research operating system. UNIX turned out to be an accidental runaway success, and many of Plan9's greatest ideas (like synthetic filesystems, bind/union mounts, its threading library, the 9p protocol, etc) found their way to more "practical" systems.

It also did have a commercial counterpart in Inferno (mostly finding use in products like telephone switches). But nowadays both remain mostly as toys for enthusiasts. You can get work done, if you're patient enough, and have the freedom to ignore things like Zoom calls or Excel files.