Lisp-based operating systems are no longer used, because they were quite complex (coming out of a research environment) and provided LESS functionality in some crucial areas (for example they were not multi-user - they were one-person, one machine, one 'world'). Additionally they were expensive.

The Xerox Lisp and Xerox Smalltalk workstations one could buy were severely underpowered (RAM, speed, ...).