Why do all apartment complexes in Albuquerque have pools?
In most places, it's probably more efficient to invest in more houses than to put pools for the same value in the houses you own. In some place, having a pool might even decrease the renting value of your house: the maintenance cost compensate the rent increase. In Albuquerque, it is possible that it's more relevant to invest in pools than in houses, hence all landowners invest in pools, hence, no more houses to rent without a pool.

With $P$ the cost of a pool, $H$ the cost of an house, $r_H$ the revenue you get for renting a naked house and $r_P$ the revenue you get for renting a house with a pool and $c$ the upkeep of a pool, every house owner is going to build a pool before renting or selling if $$(r_p - c)/P &gt; r_H/H$$

If this isn't true (and it isn't in most places), some people we choose to build a pool for other reasons but not all houses will have pools.