Also, VMS and other OSes were the ones that ran for years without rebooting. Unix at the time was not so stable. Before Tcl, John Ousterhout wrote a log-structured file system for Unix because their Unix systems crashed often enough and took so long to boot that a possible loss of data but fast boot-up was deemed better than the lengthier downtimes with the existing file system.
So the PC market went with Microsoft and its encompassing environment, much to everyone's detriment. Fortunately, we've all moved on to the web and JavaScript and everything is now sunshine and roses. :-)