In addition to the sanctifying by Church and other high authorities & institutions, with elaborate rituals and such.. up until recent times the Royalty was seen to be entitled their position because of by birthright. At first I wondered why the people would go along with such an idea. Then as I learned more about the world, I realized most families also had rights in society granted to them by birth. For example your family might have one of limited quota right to have x number of cows in your area. A right that was granted to your family generations ago and enforced by the state against those who would attempt to enter your line of work. Everything from selling salt to brewing beer to making candles was protected by licenses.
To question whether the King should be in his place by birthright, was to also question whether your family should be one of the restricted few who by birthright were allowed to own cattle in your area. Because people 'knew' deep down that they rightfully deserved the entitlements given to them by birth, by the same logic it reinforced the Kings entitlements.
Likewise in on our own times, its amazing how much of our economic lives are still through restricted licenses of various sorts. Or access to limited job opportunities like high paying state or monopoly corporate jobs, that really only can be gotten through family connections. All of these exclusionary rules are enforced by the strong arm of the state.
So when the state decides to give more of its haul in taxes to bankers or high state officials, millions upon millions who are also making more than they otherwise would without the exclusionary state policies, union contracts, quotas, funding, etc.. they might complain, but not complain too loudly. For if they complain too loudly, the state could decide that instead of restricting competition in those loud complainers line of work, maybe their profession would be better competing on an unrestricted and open free market.