What else are they going to spend their gil on in a game that lacks any significant gil sinks to drain gil back out of the system?
As for the resale market, right now the purchase timer hinders it but not stop it. If there weren't enough players willing to deal with resellers through the limitations currently imposed by the system, the resale market would have shut down by now. Since that hasn't happened, we know the resale market is healthy enough even with the current limitations.
Remove the purchase timer and the resale market blows wide open again because those limitations disappear. Anyone with the gil could be the buyer instead of just those who already own a house or who are willing to buy a FC to get one.
You seem to be overlooking that there won't be 5760 plots available for sale on each world if your proposed change is implemented. Most of those plots already have owners and SE is not going to charge their owners retroactively for any purchase price increase. It's going to be the relatively small number of plots that are demolished or voluntarily relinquished and their new buyers that would be impacted by the price increase.
How many houses per NA world were becoming available each week prior to the suspension of the demolition timer and independent of the ward additions. My guess based off what I can remember from previous discussions would be about 6-8 a week. That would add up to about 400 houses available for sale each year, again independent of any decision by SE to add more wards.
When active player populations on the NA worlds are estimated to be in the 20-25k, do you genuinely believe there won't be at least a few hundred out of the 15-20k "homeless" players willing and able to pay the reseller's fee on top of the purchase fee for at least smalls and mediums?
Resellers might not get their hands on every house that becomes available but they'll be able to get their hands on enough for reselling to remain in the game unless SE changes the system so supply meets demand.
No longer worth it to you, perhaps. But there is always someone who will grasp any opportunity for profit. And removing the timer would remove some of the headaches resellers currently have, like creating new shell FCs from scratch.
(edit: want to clarify that I'm not trying to imply you currently are or ever have been a reseller, only that in your mind it would not be worth it if it was something you had been considering)
Ultimately, we're back to SE needs to fix the system. There is no good reason to make housing a limited resource exploited for profit by those out to make profit whether it comes in the form of reselling or creating multiple FCs to run workshops and gardens. Ownership of a house should be an opportunity for every player in the game.
Let's stop dreaming up ways to make certain a broken system stays broken.