It just makes one wonder, what is the point of categories of Nobel prizes? Should they instead hand out half a dozen or so prizes each year for whatever is most important to them?

No deeper point other than the person who funded it thought these fields should be awarded and encouraged (econ is the exception).

The categories correspond to who's filling out the nomination paperwork, and voting. You might think of it as a "Nobel from physics," which only usually is a Nobel in physics.