TWA has answered it pretty succinctly. Just to put in historical perspective. Until about 5 years ago almost every brand tried to integrate its own OTT smart system into its TV's, and some were trying to make a go of doing that AND making their own OTT boxes as well. There are really only 3 viable "boxes" left, Roku, Amazon Fire TV and Apple (and in that order), while there are others out there, they are essentially dead (and Apple is on version 4 or 5 of their TV strategy and each permutation has been seen as a failure). In terms of what was integrated into TV's obviating the need for an internal box, Roku has sort of won the battle, as the majority of TV's currently sold in the US have the system integrated into them, not just TCL TV's but Philips, Hisense, JVC, Hitachi, Westinghouse, Sanyo and many more. The two LG systems have been garbage even though they co-opted Panasonic and Toshiba into it), Sony's isn't much better, and honestly the Samsung one is just OK. Google seems to be making a push again after abandoning Android TV and replacing it with Google TV, but is really an also ran.

TV's are essentially a commodity item, almost all are assembled from the same kit of parts, so for example most of the LED screens no matter which brand you buy come from maybe the same six factories (Dominated by Samsung and LG), and as noted above, a Panasonic TV might be assembled in Mexico by a Turkish company using a Samsung LED from Malaysia, a circuit board from Foxconn (Taiwan) and the majority of transistors and capacitors from China.