The Meaning of Life, the Universe, and Everything.
In pretty much every single shooting game, there is some type of bonus for shooting someone in the head--why not Minecraft?
So, I know you're thinking, "how would this be useful," and "But Minecraft isn't a shooting game," and those are valid arguments. I will explain the answers, though.
Admit it. It is pretty tough to shoot a moving target, especially when it is as small as a player's head. So it only makes sense that there should at be double damage inflicted when you go to all the work of aiming that well. Also, killing aomeone only with a bow when they have armor on is next to impossible unless you have some crazy enchantment on it. This just gives the players some incentive to work extra hard for something that benefits them. Finally, some minigames like skywars take FOREVER because people like to stay safe on their island, sniping others players from afar. If double damage is inflicted when a player is hit in the head with an arrow, slow games like that will finish quicker, letting players wait less time to play the next game.
Minecraft--Mining and Building--Not Shooting
But a big part of minecraft is hunting for food and killing hostile mobs, which sometimes requires a bow and arrow. Especially in Minecraft Minigames, the bow is used a lot. Some examples of games that include killing with bows are Skywars, Survival Games, The Bridges, Mega Walls, and that is only naming a few. Most of the games that I just mentioned are also very popular games, so they should be the best they can be, and being the best is not being the slowest. This would help speed up, and make the games more fun.
Most of the examples you gave are for minigames, not survival Minecraft. These could be added using plugins that already exist. Plus, long range sniping mobs isn't a challenge, as they don't move outside of a certain radius. Basically, The only real use is on servers, where plugins can do the job.
With this logic, sword hits to the head should also do more damage (and that doesn't require much skill) and double damage is too much: if anything, 1.5x or 1.25x + damage would be better. This is something I've been thinking as a mod: Individual hit-points, on the same entity, varying in resistance.
Minecraft doesn't need headshots. With them, they'd need to recode the hitboxes to allow the game to know what is and isn't a headshot. Not to mention it could potently make bowspamming a real tactic again.