What makes this JS implementation deserve the name "Quick"?
I noticed it doesn't appear to do JIT compilation or any of the fancy optimisations V8 does. So whilst it may start up quickly, and may interpret quickly, it won't actually execute JS quickly relative to V8, unless I missed something huge in the linked web page.
It's not at all my field of expertise, but my guess is that problems with V8 are that it's an order of magnitude larger, that it's written in C++ rather than C89, that it's more likely to make large changes to the way it works, and that it uses more memory.
All of those are good decisions to make for a component of Chrome that helps run webpages. But sometimes you'll only want to make it possible for users of your less than massive technical application to script its behavior using a language they might already be familiar with, and then those properties are undesirable.
"Quick" calls to mind something that's not just fast, but nimble.