Aces,
I would be very surprised if ANYONE instructs through "habit", The effort of just keeping the rating going means you are either doing it because you need to, or because you enjoy it. Rather than see the part timers go, who instruct because they enjoy it, I would much rather those who are only there for the hours get out, if you do not have the students interest at heart, how good is the instructing going to be? ( note I said JUST there for the hours, there are those that are going for hours, but still enjoy the instructing - and they will probably be the airline pilots of the future who still instruct part time!)