Lisp machines were clearly abandoned because of their price. Every time I find some history about someone that actually made that decision, the reasoning was exactly alike, those machines costed more to keep than the Unix ones to install, and were less capable due to outdated hardware.
Yet the essay goes all over the place, citing time to market (that was completely irrelevant, UNIX was the newcomer, Lisp machines were there already), university-based prejudice (yet every single one decided the same at around the same time), and blaming the user. The essay doesn't even talk about money.
