To be pedantic, this isn't quite correct. Syntax isn't countable like that. What S-expressions are light on is production rules. At their most basic they have IIRC 7 production rules but there are absolutely 0 languages based on s-expressions which are that simple, since it doesn't give you anything like quasiquotes, vectors, Lisp 2 function resolution, etc. Reader macros make matters much worse.
What we can say is that they are constructively simple, but not particularly unique in that. Once you get into real sexpr languages they aren't simpler than horn clauses, and are constructively more complex than languages like Brainfuck and Forth.
It's repeated a lot because it's true. The collective developer world has decided that LISP syntax is not the preference. Good if you prefer it, but you're the in the overwhelming minority.
Random example i just found via github explore: https://github.com/replikativ/datahike/blob/main/src/datahik...
You probably love it but to me it looks like a wall of text. Sure I can figure out what it does, but it gives me a headache.
To use the right words: it’s not a syntax issue, it just looks unfamiliar to you.
To this day I have to look up whenever I get back into clojure what the "syntax" is of ns, require, import, etc.
but i bet if you sat down a junior developer not yet entrenched in any style yet, they'd be able to grok lisp code MUCH faster than the intricacies of syntax of the other alternatives ¯\_(ツ)_/¯