Mostly other languages like Lua and Python also being good choices.

Lua is simpler, is much, much easier to embed into your project and is much faster, especially with LuaJIT. It is the perfect fit for this task

Too much OO can hurt performance quite badly and while some form of OO is common in the game industry there is also more emphasis on keeping things simple. Ruby is a very nice language and not a bad choice for non-performance critical code but Lua is the default choice for game scripting for a reason.

And for the cases there Lua is too simple, well there is Python. Sure Ruby does a few things better but it doesn't really have a clear advantage over Python while also being less popular.