Apartments are more useful assets to own than storage units.
A rented apartment is a liability to the tenant, but an asset to the landlord. And whether a residence is rented or owner-occupied isn't an inherent property of the residence, since it can change over time–it isn't uncommon (for a person of sufficient means) to buy a new house/apartment/etc and then rent out the old one instead of selling it.
> We generally call them "condos" when owned.
Is this a peculiarity of American English? In Australian English, "apartment" is about the type of physical structure, and has nothing to do with the building's legal structure. (What Americans call "condominiums", Australians call "strata title", but it is essentially the same thing–newer apartment buildings are almost all strata title, but older buildings sometimes have other ownership structures, for example company title.)
That sounds really confusing – owning one thing, but are talking about it as if it were two separate things. Does anyone actually talk that way?
"No."
What am I, your invited guest, to do with this information? If someone else invites me to "their condo" should I behave differently?
Perhaps there is some kind of social embarrassment in renting and thus apartment owners have come to try and differentiate themselves by using what originated as a legal term?
Homeownership wasn't always the obsession we know it to be today.
I tell you this as an American who's spent enough decades on this earth hearing English, American apartments are rented 99.9% of the time.
It's not "just vernacular", it is perfectly proper formal English. For many non-Americans – and even it seems many Americans too – calling something an "apartment" says nothing about the legal structure of building ownership.
I can find heaps of American news stories about people in the US buying apartments. Random example, this 2007 story from Fox News about the disappearance of a college student in Madison, Wisconsin [0]. It says regarding the victim that "Nolan, originally from Waunakee, had recently bought an apartment and moved to Madison from Whitewater, where she went to school". If Fox News is talking about people buying apartments in Madison, Wisconsin, then it is perfectly normal American English. Much more convincing than random Americans on HN telling me it isn't.
[0] https://www.foxnews.com/story/cops-look-at-bars-surveillance...
For the record - to non Americans (both the majority of the world and the majority of the english speaking world) - "apartment" refers to the type of dwelling, not the ownership status. For many readers this localised hidden meaning in a common term is not obvious.
Homes and condos are an asset, but for a variable portion of their ownership history, they are assets with a matching liability.
If you don't pay rent for the next month, basically you're out, but other than the time you lived without paying, some penalties and interest on the owed amounts, you're free, albeit potentially homeless.
If you don't pay your mortgaged, you'll be mortgaged, thus, potentially homeless, but depending on how much you market is valued on the market at the time it happens, and the balance of your mortgage, you can still end up homeless but still owing money to the bank.