I'd agree that Lisp was too expensive when things took off. Not just in terms of compilers, but also in terms of hardware requirements. C was a better match for the tight memory of the day.

My personal hunch about the experiment (based on nothing more than my intuition) is that people think differently, and that Lisp's syntax is a good match for how some people think, but not for how the majority of programmers think. But as I said, that's just my current intuition. My intuition a year ago, for example, was different...