This is pure speculation. My modest entry in the prediction game.
In the early days of the Apple TV, people thought Apple was going to build a real television set, not just a set-top box. One potential problem was that iDevices had a much shorter lifecycle than TVs. It was feared that the computing hardware would become obsolete faster than people would be willing to buy a new TV. One imagined solution was that the Apple TV would be a replaceable module slotted inside the TV (remember PCMCIA cards?).
Well, apparently the Apple TV is not selling well. Neither is the iPad, the other device where one can watch movies and TV series comfortably. So Apple does not have with the movie industry the kind of leverage that the iPod gave it with the music industry.
On the other hand, Apple seems happy to outsource (kind of) the sale of Mac displays to LG. So why not also let LG manufacture Apple (real) TVs, with the Apple TV part as an upgradeable module (or not). LG alone sold 28 million television sets in 2016. That would move the needle!
What about the other major TV manufacturers? Philips seems to have settled on Android as its smart TV platform. Samsung is developing its own system. Anyway, a Samsung TV with Apple inside does not sound right, does it? Maybe Sony?