Still people buy 4K TV's even if not everything they watch on that screen is in native 4K.
Go to a electronic store the most tv's they sell are made for 4K, at least here in europe, don't know from where you are.
New gen consoles & RTX 30 series support it aswell, there is even AI like DLSS & FSR 2.0 that upgrades graphics to run on similar specs with much higher details.
All that you have said is true.
However I would argue that many people keep using the same TV for more years than they would for a device like a Mobile. So while electronic stores, and similar "places" of purchase, may be stocking mostly 4K units that doesn't mean that everyone has replaced their existing TV with such yet.
[Anecdotal case in point]
I bought my own Sony KDL-55W800B back in 2014, and I don't intend to replace it anytime in the near future (unless forced to). As: none of the local free-to-air channels broadcast/stream in 4K; I own DVDs, not Blu-ray; streaming services charge more for 4K; and the Game Consoles I own work (and look) fine on what I have. And I know others in the same or similar situation.
And I live in a country known for early adoption of new technology.
