Comment by geofft

Shell is an interpreted language and its startup time is quite fast (5-7 ms on my machine, which is not a particularly fast machine).

In fact, large parts of git were written in shell until they realized that shell is only fast on UNIX because of co-evolution (you can fork without exec, and fork is quite fast), and on other platforms like Windows, existing shell implementations are much slower and there isn't a well-tuned production-ready shell that does things completely differently. Then they started rewriting everything in C.