The queen of england doesn’t have that much power, but has a defined control over the well being of an entire nation.
This control comes from the fact that, while the people in the country might fight, she represent a stable point, something that won’t change.
In italy, as in many other places, you always fight and debate about politics, and while this also happens in england, that is only part of the truth.
The queen detracts power and unite the nation, it is probably the most powerful element the polarize all the people towards the same goal.
As such, it is required for the queen/king to be impeccable, otherwise she/he would fail to do the most important thing: keep people together.