A family member I spoke with a couple of weeks ago is planning to purchase an apartment in the city to make it easier to visit their grandchildren. They won't be selling their primary residence to do this (but will be using equity from that residence). They will also subsidise the purchase via AirBnB.
This is an example of a home being removed from the stock of housing available to be used as a primary residence. I don't believe that this situation is all that unique - though thirty years ago this would have been as people in their circumstance would not have been able to do this (due to low capital appreciation and lack of a large short term rental market).