Regexes are computer programs just like any other computer program. A long program, terse syntax, embedding one programming language in another programming language, etc. are risk factors for unmaintainable code, but are manageable in the same way that you manage the risk inherent in other complex computer programs.

I did always like elisp's "rx"[1] library for removing some of the terseness. Not enough to ever use it, of course, but it's an interesting idea.

[1] https://www.emacswiki.org/emacs/rx