My understanding is that it costs the manufacturer something like $5 difference to put what's essentially a Roku into a TV to make it "smart" (which kind of makes sense as you can buy a Roku stick for $30 retails and it has to have a case, cable, box, external hdmi connector, power etc.).

The manufacturer then sells the smart tv at a $25-50 premium over the dumb version and it's a decent profit for them.

FWIW - I was always skeptical of the onboard TV smart features, but the Samsung TV that I use a computer monitor actually is actually surprisingly decent.

Could you please specify what model of Samsung TV?

It was the 2016 model of this:

https://www.amazon.com/Samsung-Electronics-UN55MU6500-Curved...

As an aside, I absolutely love using it as a monitor hooked up to a MBP.

But you probably didn't since at this point it's difficult to find a high end TV that doesn't have some crappy OS built into it.