ReDoS is one answer. Another answer is that it would effectively require supporting another regex engine with very different semantics internally. That's a tall

ReDoS is one answer. Another answer is that it would effectively require supporting another regex engine with very different semantics internally. That's a tall order, and with the existence of fancy-regex (and other engines), there's no real compelling reason to do it. You don't need to be all things to all people. Embrace the fact that there are other choices!