> But if there are no dumb TVs for sale, how do you know if that's the consumer's desire or not?

Because there was a period of several years overlap where both smart and non-smart TVs were available. If smart TVs had been a sales flop they would have been killed off like 3D TVs were. 3D TVs were being pushed hard ~10 years ago. It was supposed to be the next hot thing. But it flopped and has been all but forgotten about. Smart TV could have easily ended up the same way.