[sokoloff]

Smaller units rent for more per square foot in general, so if the building project is limited by gross-floor-area ratios, developing it into more, smaller units produces more rent than fewer, larger units.

There’s also a pretty strong effect in the US that selects towards raising 4+ person families in a house (whether rented or owner-occupied) if at all possible, so a 4 BR apartment is likely to be occupied by the (relatively) rare tenant who prefers to live in an apartment, but more likely one who is forced to by lack of option. I suspect this effect is much smaller in Asia.