You'd think he would, but......two things. One, Dean was worried to death about Bobby and that setting things straight would cost him Ellen (and it would). Dean's been known to have a blind spot where family is concerned. Two, though their histories were basically the same, who's to say Dean and Sam's history was exactly
the same at that point? They were already in the altered timeline at that point. Maybe Dean hadn't learned exactly the same lessons from, or had as much interaction with, Death.