Mostly because the people who want to introduce a "programming language" into the shell don't prioritize being a shell.
Check out the "Oh" shell for contrast. This is what a programming language looks like when you force it to conform to being a shell first priority.
https://github.com/michaelmacinnis/oh
https://www.youtube.com/watch?v=v1m-WEZz46U
This is "Scheme-like" (actually the late John Shutt's Kernel-like) but has FEXPRs so things can be redefined and evaluation can be controlled.
Mostly because the people who want to introduce a "programming language" into the shell don't prioritize being a shell.
Check out the "Oh" shell for contrast. This is what a programming language looks like when you force it to conform to being a shell first priority.
https://github.com/michaelmacinnis/oh
https://www.youtube.com/watch?v=v1m-WEZz46U
This is "Scheme-like" (actually the late John Shutt's Kernel-like) but has FEXPRs so things can be redefined and evaluation can be controlled.