Having an embedded scripting engine for large programs is nice for simplicity and keeping configuration modular - it would be messy to need to modify source constantly. It’s not an issue of it being difficult to compile something so much as it being pointlessly difficult to maintain.

do you want browser extensions to be able to modify browser code on the fly with regex? that's how you get browser extensions being able to modify browser code on the fly with regex

[1] https://www.zdnet.com/home-and-office/networking/mozilla-cha...