Why are so many heroes orphans?

Something I first noticed in my teens, and used to think about a lot.  It seems a lot of heroes don’t have parents, or that any parental figures are killed off early by the evil empire, sorcerer, or whatever.   Luke Skywalker, Conan, James T Kirk, Batman, Dangermouse, Boo (at least, I don’t remember seeing or hearing about any of the later two’s parents…)

Anyway, a long time ago I came to the conclusion that it was simply an easy way to free the hero from any family ties or responsibilities so that they can go gallivanting across the world having adventures being heroes.  Otherwise you’d have to go through lots of farewell scenes every time they go off to fight the evil lord-high-emperor-of-the-entire-universe, and explain what provisions they’ve made to take care of their families so they don’t come across as inconsiderate jerks.