Shellcode is just a horrible PL, period. Not only it's weird and unlike anything else out there, there's way too many footguns.

One can learn to use it to the point where it's usable to do advanced automation... but why, when there are so many better options available?

Because it’s never going away, and it’s always going to be there. It is the lowest common denominator. Also, a shell script generally doesn’t have any other dependencies (modulo writing one that calls jq or something). No risk of solver hell.