That's the rhetoric from young people with no strings attached. People who are older, often with families, always with local connections and long-term relationships, have far more variables when it comes to making that sort of decision.
Pay and working environment (unless either are truly terrible) are rarely even at the top when it comes to enumerating the factors that go into deciding to stay or uproot your entire life and start again elsewhere. If you have a spouse with a good job in a niche area, doubly difficult.
EDIT: Unless you live in an area where you have many nearby options, of course. But those sorts of areas are sometimes harder to move around because the competition for 'good' employers is much fiercer.