Another is that a monarch takes over the duties of Head of State, leaving those of Head of Government to the Prime Minister.
It can easily be argued that our system, with the President filling both roles, is too much for one man.
A constitutional monarch is no danger to the body politic, so there’s no reason not to have one, if the people of that country so desire. But then there’s no particularly logical reason to get one if you don’t already have one.
Yes, and I certainly understand the UK keeping theirs for tourism reasons.
Still, it is awfully undemocratic to have inherited positions. Something like a joint president and prime minister system probably makes more sense.