Actually, Lua exists all over the place, in all kinds of amazing applications - but because Lua is an embeddable VM, you mostly don't know about it that much. Its not exposed because - when you use Lua professionally, you tend to bury it deep in the problem it solves for you.
so many times I’ve read an article like this and thought that it could be even more widely useful
Lua is not widely used because it doesn’t exist. Lua {5..1-4,JIT} do exist, but these are different languages between which you and others can easily port code sometimes. It’s sort of cool in a moment, but if (when) you live through a couple of versions, that just gets old. It’s not immediately visible, so you’ll see reviews from 5 stars to zero at all times.