Hmm. Why would one expect to see space debris?

Low Density

There's a lot of space debris, but there's also a lot of space. Low Earth orbit has a volume of one trillion cubic kilometers. That means that, on average, there is one piece of space debris 1mm across per 6000 cubic kilometers, 1 piece of space debris 1cm across per 1.5 million cubic kilometers, and 1 piece of space debris 10cm across per 34.5 million cubic kilometers.

Small

The vast majority of space debris is smaller than the space between these brackets [ ]. Even with a 4K camera, objects that small aren't likely to show up.

Speed

Objects in orbit are moving quickly. At the orbit of the International Space Station (ISS), they are moving at around 7.6 km/s. That's almost 24 times faster than a .22 bullet. A camera is not going to pick up a nearby object moving that fast. Objects in orbit collide when their trajectories intersect. The typical collision speed is 10 km/s. The film Gravity gave the impression that one can see debris coming. at almost 24 times the speed of a bullet - you don't see debris coming. You see nothing and then you see the damage it caused.

So, big amount of space with a small amount of debris, usually in very small pieces, usually traveling very, very fast. It would be inordinately surprising to see it on the video. In fact, if any small objects were visible, they would be objects that have broken loose from the ISS, itself.

The Air Force tracks orbital debris, and if trajectory predictions indicate even a small chance that a piece of debris will enter an imaginary box around the ISS a few kilometers across, we consider moving the ISS out of the way.