Where did this king and queen ruling together meme originate? There can only be one king or queen ruling a monarchy, their spouse is the royal consort and has no political power. Can we blame Disney or does it go further back than that?
Cause a Royal House is a House after all and in Europe traditionally the women have being in charge of the stuff of inside of the house while the man has been in charge of the stuff outside.
So following that pattern in the the Royal House makes sense, at least if your spouse does not hate you or is plainly unfit.
The rulers have counserlors, obviously their spouse will be the a very influential one.
Showing respect for ones partner is a way to stage oneself power and image.
If you have a certain example in your mind, please, tell us.
Louis XIV was surrounded by lawyers and talent people, from Colbert to Vauban.
"I am the State" is not saying "I do whatever I want". It's saying "I represent the State of France", this doesn't mean he doesn't have any ministers working with him.
Technically yes, only one King or Queen rule his country. This doesn't mean his spouse can't manipulate him/her into doing his biddings.