Futurology

It's pretty hard to spot them, that's the main reason why. It's a known sore spot that's been talked about the past couple decades.

Bigger objects are just plain easier to see.

I think a good example is that cigar shaped rock with the Hawaiian name. Ommommuwhatever. No one has a clue where it came from or where it went. That's basically our ability to track smaller objects in a nutshell.