My current TV is 17 years old. It's 720p, plasma, and yes I want to replace it. But functionally it's as good as the day I bought it. I've used it with appletvs since the first generation - if you're not into apple, there's android and amazon boxes and sticks too.
When my appletv goes EOL, I'll buy another $99 appletv - and they're usually supported for about 5 years.
I do fancy upgrading to 4k and all that jazz, but every time I go looking at my options - they're all "smart". They're rarely supported for 5 years, let alone 17. Obviously yes you're going to airgap it once it stops being supported in 2-3 years, but having to click through one OS to get to my STB's OS sounds like such an ugly kludge.
So back to my original premise - I can't help feeling that annoying me into upgrading in 3-5 years rather than clinging onto it for 15-20, is the entire point. The primary reason I want to upgrade today is to go from 720p to 4k. In 17 years I'll be touching 60, and probably won't be very fussed about 8k. If I could buy a current version of my venerable old plasma today, it'd likely be the last TV I buy. And that's not what they want. They've seen the lifecycle on phones and they want in.
(rant aside: when I got my current set, I naively thought CableCard was going to evolve into pluggable smarts. So you could buy a brain from your cable company, or apple, or msn, or tivo, and slot it into your TV. And when Real10 needed more grunt than your card had, you'd get a new card. Instead we ended up with disposable TVs.)
Someone found a way to solve a problem they posed as a problem.
Smart TVs consolidated buying the "extra" device for older consumers... Or maybe it's as simple as it's really that's all that is left to buy?