It was written in an age where there were still plenty of computer options to go around with.
On the consumer and small business end, there were DOS/Windows boxes, WindowsNT boxes, and Macs, of course. But OS/2 was still a thing, Win95 was around the corner, and, while on the decline by 1994, Atari and Amiga devices were still somewhat sensible options for e.g. music or gaming a few years earlier.
On the corporate end, and more saliently for this specific book, you still had plenty of mainframes and such around, and an equally rich variety of options. Some of these computers were called Lisp machines, and built around Lisp rather than Unix/C. They had started to lose traction after the onset of AI Winter:
https://en.wikipedia.org/wiki/Lisp_machine
https://en.wikipedia.org/wiki/AI_winter
The authors of the book basically are Lisp aficionados who mourn the good old days when they could get by using elegant Lisp machines instead of clunky, user hostile Unix boxes.
The book itself is an entertaining read insofar as I can remember. (My memory might be playing tricks on me though; I read it 10-15 years ago.)
The authors obviously cherry pick to maximize Unix bashing. The authors make a number of very valid points - some of which still apply today. The tone is usually playful. But then, at times, contempt with a pinch of self-importance emerges, and you're left wondering why you're bothering to continue reading a 300+ page long rant... only to realize that the points made are so obnoxiously valid (or, at least, were when I read it) that you continue.
Dennis Ritchie's anti-forward passage return the favor, too:
> Your book is a pudding stuffed with apposite observations, many well-conceived. Like excrement, it contains enough undigested nuggets of nutrition to sustain life for some. But it is not a tasty pie: it reeks too much of contempt and of envy.