It is sort of weird that ALL counties still exist on having a separate head of state. They're all just doing it out of habit too.
At some point, some country is just going to be, you know what? Let's just have a Prime Minister as head of state and government. I wonder who will be the first.
Bibi tried half assedly to do it in Israel.
USA have de facto unified the two positions. The result are that half the country hate the HoS. By splitting the two position from each other you get a PM who can focus on politics, while the HoS can focus on reaching out to the entire population.