Spoked wheels aren't cast because it's hard to machine them. You can easily CNC them if you really want. But that would be insanely expensive and wasteful and not any better.
I've watched enough Chip Foose on TV to know that in the custom car world it is commonplace to start with a solid blank wheel and CNC away 90% of the face to achieve any particular design. It takes only minutes, and unlike casting or forging you do not need to purchase hard tooling for each different design.
