Why didn't Plan 9 take over the world?

Plan 9: The Way the Future Was

Reasons:
*scanty documentation, much confusion and stumbling over fees and licensing.
* In 2003 it looks like Plan 9 failed simply because it fell short of being a compelling enough improvement on Unix to displace its ancestor.
* Some Plan 9 ideas have been absorbed into modern Unixes, particularly the more innovative open-source versions. FreeBSD has a /proc file system modeled exactly on that of Plan 9 that can be used to query or control running processes.
* Experimental 2003 versions of Linux are implementing per-process mount points, a long step toward Plan 9's private namespaces.
* The various open-source Unixes are all moving toward systemwide support for UTF-8, an encoding actually invented for Plan 9.


Conclusion:
Plan 9 is not good enough to take over to the various unix world.