I think that at least part of it is APL's dependence on specialized hardware (at least back when I last encountered it in the 80s). At the Claremont Colleges, most computing access was on VAXes running VMS, although there was a single Unix machine at Harvey Mudd and Pomona College had an IBM minicomputer with 3270 terminals (plus a couple of the IBM graphic terminals) and it was Pomona's system that was the only one that had APL because the 3270s could use the specialized character set while Mudd (the science/engineering school) did not. The big language push at Mudd back then was towards APL, perhaps because a lot of aerospace companies sponsored clinic projects (all engineering students and some other majors did a sponsored real-world project in their senior year).
I remember writing some data analysis code in Fortran for my freshman physics lab and the TA was surprised to see my choice of language.
I remember writing some data analysis code in Fortran for my freshman physics lab and the TA was surprised to see my choice of language.