[btilly]

I have a simpler theory.

The law is the way it is because of the influence of lobbyists. Those lobbyists include lobbyists for companies that do things like payroll. They would like the system to be complex to provide a regulatory moat that keeps other businesses from competing with them. And by siding with this or that special interest that cares about their piece more than how sensible the whole is, the law is easy to turn into a mess.