I do know such people as well, and, yes, what the lack is flexibility. They stick to their old knowledge refusing to learn something new in order to get much better salary in some of the developing fields. It's a pity that knowing so much already, they don't want to learn a bit more to fit in some highly paid positions. Like it or not, we are no longer in times when the education you received in young age can be enough for the rest of your life.