That's true, but a naive Lisp evaluator is a) not a compiler, and b) not correct. A naive implementation of Lisp leaks memory very rapidly, and obvious memory management schemes fail. Garbage collection was invented for Lisp to deal with these problems, and even assuming an immature implementation, GC isn't trivial. The simplest implementation of mark-and-sweep garbage collection requires a lot of discipline to make sure that objects are correctly allocated so that in-scope objects are kept live and out-of-scope objects are discoverable as dead. Even if you're writing your own allocator for C, that allocator is pretty trivial in comparison.