Your code doesn't actually compile in my MPLAB XC8 compiler but should be fixable so I may give it a go. I note there are no comments in the code but the explanation text should help.
It's about 6kloc. (I don't know how it compares to Picocl feature-wise.)
It ran on those Nokia phones that had a minimal version of Java (no floats!), which was kind of cool back in the day.
Unfortunately, as with most interpreters written in C, afl finds segfaulting bugs in a few seconds. In your case at least empty variable substitutions are broken. E.g., entering
Objectively speaking, though, it seems like you're right -- historically, people have chosen Lisp-like languages over Tcl-like languages, as the latter are now mostly relegated to toy language projects like this one.