Say you bougt a house for 200K many years ago. Your neighbor bought the slightly larger house next door for 275K back then. Your house is worth 1M now. Can you move?
Sure, you can sell your house at a nice profit (and pay taxes on that!!). The neighbors house is worth maybe 1.2M now. So you can't really afford to move.
Housing gains on paper are not income and you can't cash in on it unless you move out to a much cheaper area. Otherwise whatever gains you had on paper also apply to the nearby houses, so you can't afford them.