This might have been before uLisp (definitely prior to my knowledge of uLisp), and they wanted to write the interpreter for it themselves. IIRC it had 16k of RAM, so it definitely could have run uLisp.
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I should also point out that just storing the names of all of the symbols in the common lisp specification exceeds the RAM requirements of uLisp. Obviously builtins can go in ROM, but it gives you an idea of the sizes involved.
uLisp was too large for a small flight computer I made for a hobbyist rocket - I wanted to use it but had such little RAM I had to go down to C. I think I could have ran lisp-to-c to generate from uLisp which I’ll try on my next project.
In such contexts it is more like an Assembly with a C like macro processor than proper ANSI C anyway, and if you go the code generation route, then you would be better off using the DSL capabilites from Lisp to generate Assembly directly.
[edit]
I should also point out that just storing the names of all of the symbols in the common lisp specification exceeds the RAM requirements of uLisp. Obviously builtins can go in ROM, but it gives you an idea of the sizes involved.