For a while, the appeal was that it was cheaper and simpler to just buy a smart TV that had Netflix, etc integrated than it was to put together some other solution yourself.
Turns out the reality is that the integrated smart functionality tends to be slow, clunky, and rarely updated. Now that things like Roku, Apple TV, and Chromecast are so cheap and easy, the tides have turned there.
While I was somebody that bought a smart TV a few years ago for those reasons, I've gotten to where I haven't touched those features since Chromecast launched. If anything, it's become an annoyance that my TV has a 15-20 second boot time when I turn it on. I know I've decided that my future TVs will be TVs only, and that seems to be a common theme among others I've talked to with smart TVs.