Lua used to be very popular for embedding because the runtime was minuscule so it could run in very constrained environments (like old consoles). This is mostly a non-issue these days though.
JS and Lua are very similar feature-wise and I imagine Lua hasn't gotten the massive JIT runtime optimizations that JS has, so JS seems a far better choice these days.
Once you reach LuaJIT levels of performance though it's not like you need more. If you're doing a huge amount of heavy lifting in your embedded runtime then you've probably designed the application wrong.
The fat better arguments are that it's more common and there are more libraries.
Yeah that is a good point, I also imagine lua is far easier (build/linking) to add into your application compared to pulling V8 or JavascriptCore.
So if you only need a small language to do a couple thousand lines of code in than it still might be a better choice. But for larger projects JS still seems better due to the ecosystem and knowledge available.
But if you compare some games like baldurs gate 2 where most of the event logic and quest state is in the scripting language, then maybe it is worth spending the time to add JS. But if it is like Civilization 6 where only small stuff like UI and I/O mapping is in the scripting language then it is a different matter.
JS and Lua are very similar feature-wise and I imagine Lua hasn't gotten the massive JIT runtime optimizations that JS has, so JS seems a far better choice these days.