..why would anyone in their right mind buy..
Go look at how much it would cost you to a buy a single Raspberry Pi (its capabilities are just about right for this). Then imagine what something like that would cost a huge manufacturer like Samsung (I say this part, so that you'll have some sense of how low the margin will be). That is how much a smart TV costs to make, relative to a dumb TV. On something costing hundreds of dollars, it's nearly free.
And what the game console makers, the smartphone makers, etc (and even pre-loaded OS desktop PC makers) have established over the last few decades is that "nearly free" can become "actually free" or even profitable if someone pays you to bundle malware with your product, or there's some kind of product-tying, or things like that. (So basically, damn near every expensive anything, ought to have a [potentially user-hostile] computer in it. Think of anything that costs $400 or more. That thing needs malware.) So just having a CPU can increase the revenue from the sale, so that from the manufacturer's point of view, it virtually costs less to make. So if you're in a highly competitive market, you can sell it for less.
Thus, the reason people buy these things, is that they cost less (to buy; I mean the cost at the time of the sale, not the costs of using the product).
We simply haven't yet gotten to the point where, when you first buy a TV (or a car) (or for some people, a phone) the first thing everyone knows they need to do with it, is overwrite the preloaded assumed-to-be-user-hostile software with a user-centric replacement. Fortunately, Samsung is joining Apple and Nintendo/Sony/Microsoft, and many others (this is an all-too-common thread to rehash; don't feel offended if I omitted your favorite Peoples' Enemy), in helping to teach us all this basic principle.