Previous lisps had only the list as a datastructure with a special syntax and the program was only represented as lists.

There are different "schools" now. Some argue that representing the program only with lists is more uniform and simple. Rich Hickey argues that the different multiple usages of lists in "traditional" lisps, such as in Common Lisp, imposes a cognitive burden so increase the complexity.

The Janet language for example follows Clojure whereas as Racket is still a modern language but follows the "tradition".