I haven't fully grokked it myself. But it relates to the concept and implementation of a Lisp reader.

https://en.wikipedia.org/wiki/Lisp_reader

"Unlike most programming languages, Lisp supports parse-time execution of programs, called "read macros" or "reader macros". These are used to extend the syntax either in universal or program-specific ways."

read-string is a convenience over calling read itself as it will take a string rather than needing you to create a java.io.PushbackReader yourself.

As such read and read-string were implemented as core to Clojure's self interpretation and implementation, not as part of a general safe serialization API.

Unfortunately the temptation was to reach for read-string for de-serialization in general as it was so convenient and in the core. In a dev setting where you control and trust all input that is fine. In other contexts it definitely is not!