But even if we take the MIT Lisp Machine system, which is smaller, it is still 450 KLOC. Just the microcode that implements the Lisp Machine on the CADR around 25 KLOC.

The Lisp Machine system is also _very_ complicated under the hood when it comes to the core system, and one of the reasons why Unix succeeded.

It is also a system that is a total PITA to modify in incompatible ways, since you are always modifying the running system. There is no such thing as an executable file in the same sense as on Unix that you can copy and keep around, e.g. if you modify the compiler on Unix you can easily keep a backup copy of 'cc' and keep running that when you screw up.

On the Lisp Machine you can't keep two compilers around at the same time without essentially creating a fork of it with all new names (and even then it might not work).