Why can't I use NumPy in Rhino Mac

There are initiatives (1, 2) that target running CPython in Rhino/Grasshopper, which enables one to implement numpy/scipy. I haven’t really messed with either one, but there certainly are considerable dependencies and plumbing involved, making it less than straightforward. An alternative (and arguably simpler) approach is to implement an equivalent .NET library (in this case, for instance Math.NET).