Why are black holes so difficult to detect?

Black holes are so dense that light cannot escape from them, and they are difficult to detect. Satellites above the Earth's atmosphere can detect bursts of high energy radiation given off by black holes. Dozens of stellar black holes have already been detected in the Milky Way, where there may be tens of millions more.

Explanation:

it's filtration, but this is an assumption so my apologies if i got this