Question

Why would an isolated black hole be hard to locate?

Answer 1

Since they do not emit any radiation n it is not possible to see them.

Explanation:

Indirect methods like speed of orbiting stars may indicate the presence of a black hole.
Also when matter falls into black hole from a companion binary which is red giant we can see X rays from the event horizon due to very high temperature.
Both these methods are not possible for an isolated black hole.