When one doesn’t need to be worried about being elected, one can make decisions based on principle, and the longer-term view, rather than pandering to popular opinion.

We always complain that politicians work on a two-year cycle. If your position is permanent (pending death), you escape this cycle.

See also: the House of Lords.

It’s weird to think about, and I’m a working-class Labour voter from Sunderland whose grandad was a welder on the ships, but there’s something to be said for it.

There's also the argument that if your job as ruler is known from a young age you can be groomed into the role in a way a career politician never will be. A system for choosing a head of state that requires an extensive training period and that meant they couldn't simply be turfed out on the whims of a gaggle of swinging voters has something to be said for it. But what sort of long term decisions would you have them make?

Probably infrastructure, as that takes a long time to complete, and can be made a little more effective rather than "if I can find a way to tunnel from the country to the beach, I'll get more votes" (/s)