The much reviled Global Interpreter Lock(GIL) slowed python down, but also made it really easy to write libraries for.

If you wanted to do something there was probably already a Python lib for it. Nothing else had such a rich library ecosystem. If you really need python to perform it is usually easy enough to write the needed routines in a lower level language link it in.

Python grew because it was so easy and powerful enough. Now that python loads are getting into substantial computing the efficiency is becoming an issue.