Lisp famously has one of the simplest syntaxes possible that is still structured, and one of the simplest data structures to understand. There's almost nothing to it.

And why would you introduce Lisp in a compiler/interpreter course, to people who are presumably already quite advanced in their knowledge?

Lisp is best as a teaching aid to introduce common high-level language concepts, in a way where it's clear how they all actually work in a familiar syntax- because it's Lisp nearly all the way down. (No black boxes.)

Most other languages suffer from a "trust me" problem, where students are taught what complicated things do but have to take it as gospel because they can't read the implementation, so they end up with high level concepts but no idea what's really going on to make those work, and a vague belief that "underneath" is more complicated and mysterious than it has to be. (Black boxes abound.) Indeed some students struggle to understand high-level concepts until they can see the mechanism.