Individually the poor are not too tempting to thieves, for obvious reasons. Mug a banker and you might score a wallet containing a month's rent. Mug a janitor and you will be lucky to get away with bus fare to flee the crime scene.
I read a lot of plays as a kid, but I didn't see that many plays, so I feel better-versed in film history and film structure. I just think it's easier to think in pictures.