People aren't using their internet-connected smart TVs for anything beyond, well, watching TV. It turns out, nobody wants to tweet from their TV. Or read books. Or do whatever it is people do on LinkedIn. Worse, more than 40 percent of the people who buy a connected TV aren't even using it for its ostensible primary purpose: getting online video onto the biggest screen in your home. What gives?

We didn't need a report to tell us this, but NPD provided one just the same. The report finds fewer than 15 percent of smart-TV owners are listening to music, surfing the internet or shopping on their TVs.

I think I can explain all of this with a single thesis: Smart TVs are the literal, biblical devil. (That may be overly broad. Perhaps they are merely demonic.) But the bottom line is that smart TVs typically have baffling interfaces that make the act of simply finding and watching your favorite stuff more difficult, not less.

More on Smart TVs

Why You Shouldn't Buy a TV This Year. Again

Apple Mountain Lion: The Ultimate Cord-Cutting OS

Cord Cutters: Switching Off Cable, ForeverThere are two things to mull over here. The first is why apps haven't taken off. The other is why more people who buy a TV capable of showing online video aren't watching online video. Although related, they have different explanations.

If you've ever used an Internet-connected TV, it's pretty obvious why apps for Twitter and Facebook and reading books or shopping haven't taken off: It's a lousy user experience. Sitting 10 or 15 feet from your screen and trying to interact with it is a tricky thing to do. Even if your TV has a keyboard (doubtful) and you've got perfect vision (most people do not) and you're a great typist (ha!) working with text from that distance isn't easy. The mere act of firing up those apps can be a chore compared to the ease of doing so on a mobile device. It's a far better, more intuitive experience to use the second screen — like your tablet or phone — while you're in front of the TV. Which is exactly what people are doing.

But why aren't more people using their smart TVs to watch online video? NPD attributes this in part to all the other connected devices we have — Rokus and Apple TVs and Xboxes and TiVos — that offer the same services. That's certainly part of it. But the real answer lies in its conclusion: Smart TVs are just too complicated. They have terrible user interfaces that differ wildly from device to device. It's not always clear what content is even available — for example, after more than two years on the market, you still can't watch Hulu Plus on your Google TV. At least, not without resorting to trickery.

The bottom line is smart TVs are dumb. They give us too many options for apps most people will never use, and they do so at the expense of making it simple to find the shows and movies we want to watch, no matter where they are, be it online or on the air. As NPD puts it in the conclusion to its report, "OEMs and retailers need to focus less on new innovation in this space and more on simplification of the user experience and messaging if they want to drive additional, and new, behaviors on the TV." Which is a more polite way of saying, clean up your horrible interface, Samsung. (And Sony and LG and, well, everyone.)

We turn to TV to relax and unwind and enjoy ourselves at the end of the day. Our TVs should be easy and pleasant to use. But instead, all too often, it's the most complicated device in the home.