Most Excel users (not the power users, just the 1.1 billion everyday ones, including many of the enterprise ones) don't know how to program in any language. You're coming at this with a HN mindset.
"Python vs Lua" is not even on their radar. And even if it was, their criteria would be dominated by platform lockin and compatibility with other licenses (e.g. commercial SQL, Tableau, MSFT, etc.). Not by "which open-source language?"