The Shining

I’m watching The Shining. Jack is ranting about how important it is that he honor his employer’s contract, right after typing out a hundred pages of how all work and no play makes him a dull boy. Then his wife hits him with a baseball bat. And yes, I’ve noticed Kubrick’s constant use of Native American leitmotifs contrasted against the symbols of Western imperialism.

Why does it seem that Jack Nicholson is always in the role of characters named “Jack?”