For a long time, the answer was probably performance. Lots of people were trained to use Lisp in their computer science courses, and lots of people admired it. But it was never anywhere near as fast as C, and in the seventies and eighties squeezing every darn bit of speed out of your hardware was what counted.

The language had another chance in the nineties, when it became important to save not just execution time, but the programmer's time also. This is when interpreted languages like Perl and Python started showing up in a big way. I'm less confident why Lisp lost out that time, but its weird syntax is probably at least part of the reason.