> Richard Gabriel founded a company to write software for Lisp Machines,
The company Gabriel founded (Lucid Inc.) was never supposed to write software for Lisp Machines. Its mission from day zero was to develop a Common Lisp implementation for stock hardware (SUNs, etc.). Symbolics, the Lisp Machine maker, refused to fund a portable Common Lisp implementation (which Gabriel and Benson, the latter then at Symbolics, proposed).
> found that all of his customers would rather just write in C, pivoted it again to do a C++ dev environment, and eventually went out of business
Actually the Lisp business of Lucid Inc. financed the C++ development.
It was a gamble. They easily could have continued to develop and sell Common Lisp (their main competitors from that time, Franz Inc. and LispWorks are still alive) and stay in a small/shrinking niche. But Lucid tried to diversify and to grow. The idea was to write a C++ environment with a similar and improved development experience as a Lisp system. They used the cash cow they had and eventually sunk the whole company when the C++ system flopped in the market. Their C++ system (Energize) was very expensive, technically complex, ...