I don't think it's fair to paint this as unique to US citizens. I'd go as far as saying this is generally true across the world, with few people protesting state sanctioned violence abroad, and significantly more people protesting domestic state sanctioned violence.
I don't think that's unusual. I think it's normal that we care more about our own lives than we do others lives, we care more about people dying at home than we do abroad.
I'm not saying this is a good thing, but it is normal human behaviour. A good example of this is watching how peoples perceptions of this latest coronavirus unfolded.
There's too much going on in all of our lives to have time for every bad thing happening elsewhere. You pick your battles. That's ok. You still have to live your life for yourself at the end of the day, nobody else is going to live your life for you.
> few people protesting state sanctioned violence abroad
I was referring to their local state committing acts of violence abroad. As you correctly note, the example mentioned is not the only one of its kind. This happens far too frequently. It falls into the "every bad thing happening elsewhere" bucket.