Why not Python? Syntax is much cleaner and there’s nothing you can’t achieve. Even performance is on par.
Also I don't like the syntax of python
Meson is written in Python and isn't dead. However, Meson requires a partner to actually build things--something like cmake or ninja.
However, I think the original poster meant "Why Lua instead of Python?" And the only real answer is "Because that's what the author wanted to use."
For auxiliary things that you don't become expert in like source control, build systems, etc., it's vitally important to have a vibrant community around it so you can simply look up the answer and get back to your job. Or, you can have an emergent AI robot like Randal Schwartz, Wietse Venema, or Armin Rigo handle that support (seriously, do those guys ever sleep?). But you need to have one or the other, and Scons never seemed to.
I really don't understand why Scons never took off. I think it was simply that it was too early. Nobody actually cared about cross-platform in the sense of Windows/OS X/ Linux. Of course, Blender did care about that, and still dumped it. So, YMMV.
I think people only started to genuinely care about "cross platform" when developing both cloud code and client code simultaneously became a thing. And then that accelerated with the polyglot of languages layered on top of Javascript.
It's nice and I could imagine it getting some adoption because of its flexibility, but my C++ projects tend to have their needs met with Makefile.