Python has a much larger and more mature ecosystem. Lua barely has a functioning package manager.

It's still early in development, but the new package manager Lux looks promising: https://github.com/lumen-oss/lux

Don't forget it's much more productive writing a script in Python to parse a text than Lua due to its huge feature-rich syntax

Lua is great when you need an embedded language.

That's it. It's not great on its own, in my opinion.

It becomes really gnarly if you have a bigger Lua codebase.

Rebol is the cleanest/greatest language I've read code for but the VM is the slowest VM I've ever wrote code for, mind you I only did the first 10 exercises of euler but the only thing that has it beat is writing a shellscript that forks to dc/bc on each math expression.