That part of the story is key: the fact that nobody knew how to treat mental illness back then. So it wasn't much fun to be around the palace when Justin II went into full crazy mode -- it's said that when his servants were rushing around trying to restrain him, he would fight back by biting them, often on the head. Eventually, the servants had to go to greater lengths to entertain him, and came up with a solution that would appeal to any toddler -- building a makeshift throne on wheels and pushing Justin around the palace on it, to his great delight. As John of Ephesus puts it, "... having placed him on it, his chamberlains drew him about, and ran with him backwards and forwards for a long time, while he, in delight and admiration at their speed, desisted from many of his absurdities."
"Couldn't you just ride hookers like a regular monarch?"
Are you imagining this? You have an apparently very mentally ill man who A) nobody knows how to treat, B) has the power to have you imprisoned or killed if you cross him, and C) cannot be removed from power. You have a palace full of underlings desperately trying to keep a lid on his madness. Let's put it another way: At some point, a legend even arose that Justin II actually ate two of his servants. And there wasn't a goddamned thing anybody could do about it.