Thinking you are too smart leads to all sorts of trouble, like using C++ and being proud of it.
If you think your intelligence is a limited resource however you'll conserve it and not waste it on tools, process and the wrong sort of design.
Even if we decided to use Zig for everything, hiring for less popular languages like Zig, lua, or Rust is significantly harder. There are no developers with 20 years experience in Zig
"We're going to need to fit parts of this into very constrained architectures."
"Right, so we need a language that compiles directly to machine code with no runtime interpretation."
"Which one should we use?"
"What about Rust?"
"I know zero Rust developers."
"What about C++?"
"I know twenty C++ developers and am confident we can hire three of them tomorrow."
The calculus at the corporate level really isn't more complicated than that. And the thing about twenty C++ developers is that they're very good at using the tools to stamp the undefined behavior out of the system because they've been doing it their entire careers.
They never wanted to be in a situation in the embedded architecture where performance was dependent upon GC pauses (even incremental GC pauses). Their higher-level abstraction has tightly constrained lifecycles and is amenable to static analysis of maximum memory consumption in a way Lua is not.