Because introductory material tends to live long. It is also used for non-list data structures. Sometimes in CS education Lisp is/was used to teach new stuff,

Because introductory material tends to live long. It is also used for non-list data structures. Sometimes in CS education Lisp is/was used to teach new stuff, making sure that students were challenged beyond their comfort zones, for example by reinventing the basic machineries from a few abstract principles. Typically Lisp was not used as a programming language, but as a device to teach new ways to think about computation: algorithms, some basic data structures, control structures, functional programming, ... Today you'll see other langages in CS education, with other goals. See SICP and others...