One thing I do not understand: If a black hole in line-of-sight increases intensity, the intensity for other view points must decrease (the total number of emit

One thing I do not understand: If a black hole in line-of-sight increases intensity, the intensity for other view points must decrease (the total number of emitted photons needs to stay constant). If black holes make up a substantial part of the dark matter, there should be (statistically) few in the line-of-sight and many more slightly off. Therefore I'd expect that this cancels out. Does anyone know how it is accounted for this?