Because writing your own scripting language is difficult (I've done it, it's really interesting so I'd say definitely try it once at least, but it's hard as hell to get something working well), and since Lua provides a lot of features that a basic (I mean feature-wise, not syntax) scripting language would not offer (tables, for one -- they're extremely useful). Also, if you want, you could actually write a little game-making tool that uses Lua for scripting and then write your own little level editor and such and then never have to redistribute the source, but only binaries (I've thought about this ;) ).
In any case, if you don't want to use Lua or you can't think of a good reason to use it, chances are you don't need it. I'm not using it for my game because I don't need it to be modifiable (yet, if the time comes that I need it then I'll add it).
In any case, if you don't want to use Lua or you can't think of a good reason to use it, chances are you don't need it. I'm not using it for my game because I don't need it to be modifiable (yet, if the time comes that I need it then I'll add it).