It's immutable, has bracket syntax for data structures, and most of its standard library has very sensible naming and nil-sentinel conventions. The result is that it's astonishingly easy to read and write. The data structure sharing under the hood also keeps it performant. Finding and obtaining packages with its build systems is also easy.

Scheme gets close but has some odd naming conventions and completely wild conventions for packages (SFRI, etc). CL's entire library is full of incredibly odd names first established at the very advent of computing. Using it can be...dense. And inconsistent, since it's not purely functional and has no dedicated data structure syntax.