In all fairness, I can see wanting to, say, downsize and move to a more walkable community relatively nearby. (Or, for that matter, move out of an expensive urban condo and move somewhere with more room--although that will harder in the Bay area specifically.) To the degree that market value of the two is similar, the financial hit will be substantial.

But a lot of this is true with moving generally when you're living somewhere that's OK but isn't really optimal for you any longer.