Unique state government

[Foucaulf]

The lesson from this whole discussion (for the OP) is that state governments are fairly distinct. There is a struggle between the legislators and the executive in all forms of representative government. Whereas in a parliamentary system conflict resolution is flexible (motions of no confidence), in a separation of powers system both branches limit the other through dissolving executive power among many people, changing election rules and broadcasting referendums.

There's your explanation for why there hasn't been changes in the governing system; the checks and balances are written in regulation and not in custom. Just as parliamentary legislators can backstab their leader when most people don't want that, interest groups can abuse the diffusion of executive power to chain the state to their demands.