I wish it were still possible to buy a truly dumb TV. HDMI inputs are all I need. Plug in my Apple TV and it's done. When the Apple TV becomes obsolete, I upgrade it instead of replacing the whole TV.
Smart TVs also have security and privacy concerns. Complete, total fail.
It's all about money. TVs barely make the manufacturers money in themselves. Smart TVs are exactly like the bloatware of PCs, they bring the makers much needed revenue both via commissions that are paid by services like Netflix and Amazon, and also by selling viewing data to advertisers.
You can indeed buy dumb TVs, look at the commercial models intended for hotels.