I suppose it has to do with the Schwarzschild radius of such a black hole being really small, I guess it would be something like 10^-8m according to https://en.wikipedia.org/wiki/Schwarzschild_radius which means almost nothing would fall inside its event horizon, and it probably would not collide with anything.

However, the gravitational pull of an asteroid would not be negligible, so I guess it would have a big impact pulling things towards it.