Developers many times in higher density areas don't often "sell" apartments. Rather, it is many times a lease. This doesn't necessarily help new families that want to purchase something for 100k, as their rent would keep them from making this into any investment.

In addition, to making something split into quarters each time it's "sold and redeveloped" isn't possible, as you'll run into a lack of space at some point. You could potentially do this one time.