Why don't Samsung and LG make streaming boxes?

Not long ago, I thought of smart TV software--especially from the likes of Samsung and LG--as something to ignore. Dedicated streaming devices such as Roku's Streaming Stick and Amazon's Fire TV Stick offered slicker interfaces and better app selections, which made me wonder why TV makers even bothered making subpar software. A funny thing's happened in recent years, though: Smart TV software from LG and Samsung has actually gotten pretty good. Now, I'm wondering why those companies don't take a page from Roku and Amazon, and put their software on external streaming players. To be clear, I don't own any Samsung or LG TVs, so I haven't lived with their software like I have with all the major streaming devices.