The picture on a standard TV screen is updated 60 times per second. For the human eye, pictures that appear faster than 50 HZ are seen as continuous motion. And dogs see separate pictures at 75 HZ, because their eyes are designed to react to motion. This is why the video on the screen is probably seen by dogs as separate pictures: the animals most likely see this motion as unrealistic, so they are not interested in it. But modern technology allows us to make high-res screens: this video doesn’t seem to be unrealistic to our pets and seems to hold their interest.

Another reason why dogs don’t watch modern TVs is that the screen is at a level that is comfortable for human eyes. If you put it on the floor, your dog will most likely be interested in what is going on.