Like other have said, the #1 reason is probably just being part of the python ecosystem. But there were other reasons as well: there has been a big push in academia where MATLAB was used extensively to use Python when it became available (because its free and open source; but also many licensing restrictions around MATLAB). So there has been a significant investment in the python/numpy ecosystem from both academics and industry players who don't want to deal with these licensing issues (e.g. Oil and Gas companies).