I don't see those 2 things are related though: LISP vs Interpretation of computer programs. That's the issue here.
See ? The book title has no mention on LISP, it's to teach Interpretation of computer programs right ? Why do readers need to learn something else (like LISP) ?
Probably because computer programs need a concrete representation, to actually have a structure and get to the business of saying things about it and interpreting.
Something other than Lisp can be chosen. (I seem to recall the MIT course is based on Python now.) Using something else would just add a lot of bulk to the book about parsing; you'd need chapters on automata theory leading up to lexical analysis, parsing techniques and so on. The output of the parser would be Lisp, and so then the structure and interpretation part would begin there.
They answer the “why Lisp” question right at the start:
> If Lisp is not a mainstream language, why are we using it as the framework for our discussion of programming? Because the language possesses unique features that make it an excellent medium for studying important programming constructs and data structures and for relating them to the linguistic features that support them. The most significant of these features is the fact that Lisp descriptions of processes, called procedures, can themselves be represented and manipulated as Lisp data. The importance of this is that there are powerful program-design techniques that rely on the ability to blur the traditional distinction between ``passive'' data and ``active'' processes. As we shall discover, Lisp's flexibility in handling procedures as data makes it one of the most convenient languages in existence for exploring these techniques. The ability to represent procedures as data also makes Lisp an excellent language for writing programs that must manipulate other programs as data, such as the interpreters and compilers that support computer languages. Above and beyond these considerations, programming in Lisp is great fun.
See ? The book title has no mention on LISP, it's to teach Interpretation of computer programs right ? Why do readers need to learn something else (like LISP) ?