Is there a good reason to use Lua? Javascript is pretty much the same and Guile is not only lisp, it is also designed to be used as a scripted language.
Besides the easier embedability (it's plain C with no dependencies and MIT licensed), it's (subjectively) a nicer language than JS and more accessible to the general public than Scheme/Guile, while being just as powerful as both.
And for some reason I can't pin down, it's just fun to hack with.
Lua's runtime is small and easy to embed compared to something like V8. It's also written in ANSI C. I don't know about Guile.
Much easier to embed in something else or to embed something else in it. JavaScript is possible in principle but much harder. More friendly to use than a Lisp for most people.