The desire to have those ffxiv houses reused
We were originally warned about housing reclamation in December 2013 in the 2.1 patch notes and that it'd be coming with 2.2, but there were so many complaints about it that they indefinitely shelved it and that never happened.
But then after multiple blog post complaining about inactive houses and the desire to have those houses reused, they reworked it and we were told back in October 2015 that housing reclamation was coming with 3.1. This was then confirmed in the 3.1 patch notes. Both of the those links say about if you don't walk into the house with 45 days it will be demolished and if it is demolished you have 35 days to collect your items/80% compensation money.
They do send two emails to the email address on the account before it is demolished and I realise you've said you didn't receive any email so I recommend checking your email address on the account is still valid as well as if it's been traping their emails in any junk/spam folders. Failing that, shout at your email provider as they might be running their own block list.
Housing demolition was also posted on the launcher at the time as well so everyone playing was actively informed (and having a working email address should have informed everyone not playing, but there's only so much Square Enix can do to tell people...)
The housing reclamation started with 3.1 on 9th November 2015, but due to the Kumamoto earthquake in Japan it has actually been suspended since April 2016 and has been repeatedly pushed back and won't be started again until 3.4 (27 September 2016). The free game time you recently got was due to the Free Login Campaign and was for 5 days since 25th July 2016. This unfortunately wouldn't have helped you with your house as that would have been demolished at somepoint between November 2015 and April 2016 and then the items/money deleted 35 days after that.
Well I appreciate that's a personal opionion, but there's 45 days before anything happens, an in game warning, 2 email warnings and even when it is deleted, you still have 35 more days to collect. After that yes it is gone, but that's quite a long period of time and all you have to do to save the house is walk into it... (or talk to the vendor to get items back)
I'm curious to know how you came up with such an exact figure, but although I don't know the definite answer to your question, I suspect it's nothing to do with data storage and more because they want to motivate players to login (and play?) as well as if they can ditch the data it's one less thing for them to have to worry about storing/converting/updating in the future. Also housing was originally supposed to be a massive ffxiv gil sink (so many things put money into the game, very few take them out) so they want to remove as much ffxiv gil as possible to help slow inflation. Getting back 80% of the ff14 gil was supposed to be compensation, but now of course every player wants that 80% back and won't just relinquish the plot for nothing knowing that they could get money. Deleting the money after those 35 days allows Square Enix to have that Final Fantasy XIV Gil sink again.
They already get a lot of stick for the Mogstation and at least everything on that you buy is untradeable. If they had a paid restoration they're essentially giving you money/items that are tradeable, for a real world price. Obviously they are items that you once did own, but it's no longer acting as the ffxiv gil sink it was and I can only imagine how many accusations and money grabbing there would be about SE still having the data and only handing it over after you hand over a fee etc.
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