The fundamental issue I believe they all had is lack of community. There is a quite large community of folks using Python for scientific computing. Many are not professional developers but rather scientists / engineers who aren't as open to jumping around to different languages as a developer would be.
These issues combined with the fact that Ruby is mostly pigeon-holed as a web only language would make replicating the community that the NumPy/SciPy/matplotlib stack enjoys almost impossible.
It also doesn't help that such capability have to be implemented as C extensions due to performance requirements. This greatly limits the number of developers that would/could work on such a project.