Why has Python been backed by google and become so rapidly popular and Lua has not? 

Do you know why Lua has stayed in background?

I really love Lua, but it does have some real limitations, and as others have mentioned they derive mostly from Lua's origins as a configuration file language and then later as an embedded scripting language.

Because of the goal to keep Lua small, there exists only a very tiny standard library, that has only bare bones functionality.

This has lead to an unfortunate culture in Lua circles where Lua developers like to re-implement the functionality offered by many other language's standard libraries themselves rather than working collectively on a universally accepted set of core libraries. 

Things like multi-threading, regular expressions, platform independent file access methods, and even bit operations (until 5.2) ere all "not included" since they would make Lua much larger and slower. Sure you can get libraries do so these things - but then those have independent maintainers and quality levels.

Don't get me wrong. I love Lua for the same reasons I have just listed.
