Its not hard to think of things that meet both of those features that are still better mnemonics for things that are common-language descriptions of what the function yields (e.g., cfc/csc or c1c/c2c for "cons first cell, cons second cell")

car and cdr are mnemonics related to the particular instruction set of the first computer on which Lisp happened to be implemented, which is great for people with a background with system programming on that system, but not so good for anyone else.

They're entrenched enough in the language that they are worth changing unless you are intentionally building a new Lisp-like language from scratch with some other main motivation and the change is just a side issue -- and it is clear that having something that doesn't imply list semantics for cons cells like first/rest does is good -- but car/cdr aren't a particularly good pair.