You've hit the nail on the head. It's the inability to ship product from a Lisp machine that killed the idea. The fungibility of Lisp all the way down turned each machine into a one-off lab of its own. And this tech arrived after the industry had started moving from bespoke solutions provided by hardware companies to packaged software from specialized firms. Since Lisp machines aren't good at maintaining a duplicatable environment, they're not terribly useful for commercial software production nor as a distribution target.

Source: I was a mainframe compiler developer at IBM during this era.