Originally housing was indeed locked to FCs only, and I seem to remember there being a member requirement beyond just founding. SE listened to what people wanted then and caved, opening up housing to individuals.
Then people complained that RMT peeps are house flipping, so they added random timers.
Then people complained that individuals can purchase so many houses, so that has been updated:
(source link)
The gist is if you own an FC with a house on one character, an alt can not purchase the FC house...but this is easily loopholed by having someone else buy it for you. Also an alt can not purchase their own house, assuming these restrictions are indeed in effect. (So current limit should be 2, but with some effort, you can get 9).
At this point I would not be surprised if SE just threw their hands up and said “to hell with this”, because unless they have instanced housing for 100% of the population, no one will ever be satisfied.
...and we will keep getting posts like these every week.(not that you are wrong to post, just that we are collectively shouting into an endless void of a problem at this point)