I also don't see what is immoral about these videos.. National Geographic has been producing them since I was a kid. They are generally considered educational.
I suppose this particular example is a poor one of what I am thinking.
I am thinking more of someone doing this for their own entertainment not for educational purposes. Getting enjoyment out of another living thing's pain. I could be wrongly associating this with psychopath who is more directing (or encouraging) this sort of film than one filming for the pure education of it - I suppose because typically a kitten is a domestic pet rather than prey for an alligator.
There is a big difference for example of Faces of Death and a National Geographic educational documentary.
Typically National Geographic is not filming domestic animals being eaten by wild animals - they are filming behavior of wild animals.