alt Hacker NewsAPL suffers from the same apparent problems as Perl: They have friction coming from an unconventional syntax that's hard to understand without knowing the language beforehand, and when faced with competition, people went with the path of least resistance.
* Out of all people, and especially in the newer generations, it is increasingly uncommon to find someone with a desktop or even a laptop.
* Out of them, very few decide to do anything with it besides checking mail, social media, the web or play games.
* Out of them, very few decide to learn a programming language.
* Out of them, very few decide to learn anything besides Javascript or maybe Python.
* Out of them, very few decide to learn anything besides Java/C#/C++, learn algorithms, or learn tools like Vim or Emacs.
* Out of them, very few decide to learn anything besides Rust/Go/Haskell/Lisp/Scheme or even Fortran.
* Out of them, very few decide to learn a language with an alien, symbolic notation that resembles a code golfing language, and which, too, requires them to possibly learn a completely new keyboard layout to type with proificiency.
Not trying to discredit APL's contributions to functional programming and the like, but from the letter, it is pretty obvious Djkstra had little respect for friction. Not saying that he's right to dismiss it outright, though.
Now that I think about it, and I don't know if this exists yet, but APL would probably very much benefit from having a Scratch-like or Factorio-like visual editor paired with a touch interface. You would drag and drop symbols, and long-pressing a symbol would popup its definition.
You could also probably do nice things with the symbol "icon blocks" themselves, and provide them with colors or different visualizations to convey different contextual meanings.