That is one reason. Others are they got a job in a different city. Their health declined and so they can't live at home. They got married and don't need two houses. If you cannot think of a half a dozen others in the next 10 minutes either you didn't try or your need to practice creative thinking.

The reasons are not important for this discussion though - all we need to know is some people have other pressures such that the one I listed isn't compelling to them.