Because there's no value in having a word for a situation that basically no-one is in? Because despite your sophist argument there are huge practical differences between what normal people call "renting" and what normal people call "owning"?
If I buy a computer, I own it.
Far from a 'situation that basically no-one is in' I would say. I suppose what you meant is that basically no one really own their house. Well if it's the case, why use the word anyway?
Words have meaning. You can't just decide to apply a word to a situation where it doesn't apply and call it a day.
Taxes too are orthogonal to ownership; where I live people treat the local government tax as another utility bill, like water or electricity (so when renting sometimes the landlord pays or sometimes the tenant does). If I owned a car I'd pay tax on it - but if I leased a car I'd also pay tax on it in the same way.
Words have meanings but are necessarily simplifications (just as a map cannot capture every detail of the territory). In legalese I lease my flat - but in English I own it, because how I use it and what I can and can't do with it has much more in common with something that I own than with something that I rent or lease.