[TheRealPomax]

If your ecosystem is JS, having a JS based compiler is pretty convenient. As long as it's just "slower by some constant", rather than by a runtime order, the fact that it's not as fast as yacc/bison etc. is pretty much irrelevant, so being able to keep everything JS is quite powerful for people new to the idea having started their programming career using JS, as well as seasoned devs working in large JS codebases.

(and you can always decide that you need more speed - if you have a grammar defined, it's almost trivial to feed it to some other parser-generator)