The servers are overpopulated with players who will not stick around in-game. After a full month of players getting fed up and leaving, housing will be wasted on players who no longer play.

Benefits to waiting on housing:
+ Less competition from people who won't stick around
+ Less crazy queues of 1,000 to 5,000 players (read: housing purchase RNG)
+ Less angry players for server crashes
+ More developed community areas who stick around
+ Commitment to the committed player base
+ More opportunities for established FCs to develop community areas

We all know the craziness of Stormblood launch will die in a month. Why put players in a position to compete with them?