For non-technical users, having one UI with all their streaming apps built-in is honestly a useful feature. The problem is all the other spying, hijacking, slowdowns, and other bullshit. But it's often a desirable feature for many users at its core.

For a technical user: the smarts often serve no point, we already have a streaming solution. Unfortunately, higher end TVs with OLED panels and the such come with "smarts" built-in. So the best you can do is ignore it and hope the firmware updates (that you install over USB because you don't trust it with a wifi connection) don't cause a ton of UI slowdown over time or otherwise cripple the TV. But if we could buy a dumb TV with the same features, we would.

It's so you can watch YouTube and Netflix without plugging a computer.

Generally speaking "smart" means "quickly becoming obsolete". Cars a few years old now have built in unwanted/unusable satnavs.

There is little point if you have a smartphone and chromecast. But a built in chromecast, or built in airplay video receiver is convenient. Few people have (or want) a dedicated PC to use with their TV.

The reason technical people (even those few that do have a pc connected to it) will, and should, buy smart TV's is because they are the most widely sold and therefore by far the best screen for the money. Large computer monitors or signage screens aren't as good or cheap as the most sold smart tv in the most sold size. They are extremely good for the price. If you don't want to use any smart features, most should work fairly well when operated without internet and just connected to an external input.

The real point: so you don't have control of your tv and things on it can be directed in the financial interest of the people who "sold" it to you.

The other point: There's not really an easy PC solution. The closest you can get to one is Kodi, and in my opinion it is bad. Not that they haven't put an enormous amount of work into it, but the UI is very unpleasant. Their idea of what people want out of a television interface is violently different than mine, and the configuration is absurdly opaque.

I would love a modern "non-smart" tv, but do they even exist?

It's the reason why I stick to my Sony Bravia from 2009 until it dies.

I have two LG Smart TVs with webOS.

While both TVs have a PC connected, it's far easier to use the built-in apps to watch things like YouTube and Netflix.

The apps support 4K without any fuss (which is often locked away on desktop OSes due to DRM).

The LG magic remote is pretty cool, it works a bit like a Wii remote, so you can quickly point to things on-screen.

Most people I know don’t have a PC or don’t have a PC they can easily connect to a TV as it is in another room and not easily moved.

For those that do, such as those with a laptop, they don’t want the inconvenience of connecting it to the TV to open up Netflix to watch The Crown.

I don’t want to connect my laptop, because my kids might break it. Having just a tv with limited control is perfect for kids.