Once upon a time there was a guy named *. This * was very rude. If * happened to meet another person, such as ;, he would beat up on them. One day, * was beating up on ] when he felt the world twisting and distorting around him. He was pulled through a rip in space/time and ended up in some kind of box. To his left was a yellow word, and to his right were lots of blue words, and far off was another *, which will be named **. * realized he was being used for others' entertainment, and wasn't happy, so he tried to move, but he could only go up, and not even when he wanted to. Eventually * and ** got to the top of the box. They looked at each other with tears in their eyes and suddenly, they both became better people. Then they blinked out of existence. Where they went? No one knows. No wait, he doesn't know either. Or maybe he does. We'd have to ask.
Asterikses are the bullies of the text world, and when we use them in MD, it makes them nicer before they go away. So that's why everyone uses *. They're really just trying to make the world a better place, even if it isn't their world.