Finally got around to reading this. One thing really struck me:

So what to do, let’s start with a “hello world” program, in RPG. First I made a new library called mylib using the CRTLIB command, in which I added a few objects. CRTSRCPF file(mylib/qrpglesrc) test(‘RPG sources’) CRTSRCPF file(mylib/qrexxsrc) test(‘REXX sources’)

So, the author picks RPG to write their code in, and is forced to construct a bundle containing a placeholder for super simple, approachable, easy to learn REXX code… and then ignores it? :)

Why? :)