Whats tricky is getting the investment to continue to be good once you are in the condo stage. So many condo owners hate owning condos because of how hamstringing it is. It seems like a natural march that one day a low density apartment will grow to a high density one, but how does that happen with condos? A few might not want to sell or go along with whatever change to the building and could hold up the entire process. Its like the situation where your nimby neighbors won't let you turn your home into an apartment, but now these people live in your damn building with you too. Its part of the reason why a lot of buildings in nyc are so old, turnover is tough when you have a building full of people already.
Doesn't need to be easy for any particular condo -- just needs to be more appealing to own (in) a 4-plex with a yard than a larger faceless tower?
You can't exactly force people to sell SFHs either, but that doesn't stop developers from finding a few adjacent parcels to join together. (Rather, it's not the difficulty that stops them, it's typically zoning.)
