I never said the gil-sink was efficient. On top of that, if everyone could get a house then yes, all of the housing items would be in more demand, meaning a higher price. But when people find that out, they'll flood the market with housing items, tanking the price into uselessness.
It's one of the few Gil-sinks that are actually in the game that can actually have a decent go at chipping away at the monoliths that is player funds.
But another caveat. If housing was openly allowed to all (And, for the sake of this example, go with anothers recommendation of simply giving everyone an apartment for free) then there goes.. In fact, lets do some math.
For examples sake, say Balmung has 10,000 players concurrently. All of them not owning a house or apartment.
Apartments are currently at 400K gil. A rather modest sum to most, but a mere drop to others.
Then they make the switch and everyone gets an apartment, instead of buying them.
Congratulations, you've just ensured that 4,000,000,000 gil was just kept in the games economy by that choice (And that's just Apartments, think of the number if it were smalls / meds / larges.). On one server alone. You can guess just how much of an issue that could be when SE is trying to price things to accomodate the masses. On top of (going with another recommendaton. Gil-taxing on housing) that large gil still being in the system means the Tax% of housing and apartments would be astronomically higher than it SHOULD be.
And lastly, for housing to -BE- an efficient gil-sink (by SEs standards at least), then there needs to be a limited number of them so people would try to throw as much gil as they can at it. Or prioritize getting a house over doing missions or FATEs or gathering / crafting. Ultimately lowering the gil/hour people make because they're pre-occupied in something that doesn't give them anything and instead, takes it away. Auctions would be the better call for gil-sink, but I've already gone over the minefield of issues that particular "suggestion" gets in another thread, so I don't care to repeat myself. All I'll say is that it's easily abused, just like the current system.
EDIT: Forgot to mention. If there's a limited resource, it ensures a sense of urgency when a plot opens up or becomes vacant, ensuring that people who want the house will go to it (on average, at least).