Parenthesized sexprs are easy to parse (by both machines and humans) and Lisp text editors already have many convenient ways to work with them. There are though some interesting alternatives such as sweet-expressions[1] and wisp[2], but not too many people care about these.

[1] - https://srfi.schemers.org/srfi-110/srfi-110.html

[2] - https://srfi.schemers.org/srfi-119/srfi-119.html