I think even back in 2010 (which ironically when I was getting into scientific Python to replace MatLab scripts for labs), numpy was table stakes for any implem

I think even back in 2010 (which ironically when I was getting into scientific Python to replace MatLab scripts for labs), numpy was table stakes for any implementation that wanted to be used in scientific Python communities (note that these started in the 90s). Whether the scientific Python communities were big enough then to prevent Unladen Swallow succeeding I don't know, but it would be interesting to compare the Python C API, HPy, and the C APIs (if any) of Perl, Ruby and Tcl (given PDL existed but seemingly failed to be adopted, and Tcl was widely used in science software but also seems to have died out), and see if there was anything about Python's one that caused it to be adopted so widely (my feeling is Java's lack of scripting and baroqueness ruled it out no matter the state of JNI).