I mean an asteroid the size of a bus is messy for your local area if it decides to land there, but in the terms of size of things in space is nearly undetectable. Space, even our local neighborhood is unbelievably huge.
Think of trying to find a bus that could be anywhere on earth that is moving so it's not easy to keep track of and is painted in a way to be camouflaged with its environment.
Now instead try to imagine looking for that bus on Jupiter. Gets way harder. But it's way bigger than that, your looking for a black dot in the size of an area of millions of Jupiter and just hope it crosses in front of a star so you can track it.
Think of trying to find a bus that could be anywhere on earth that is moving so it's not easy to keep track of and is painted in a way to be camouflaged with its environment.
Now instead try to imagine looking for that bus on Jupiter. Gets way harder. But it's way bigger than that, your looking for a black dot in the size of an area of millions of Jupiter and just hope it crosses in front of a star so you can track it.
Most problems involving space are insanely hard.