Well, consider that the speed of light itself is pretty slow, relative to what people's perception of the speed of light is. Even if you had a spaceship traveling at 99.99%, it'd take a surprisingly long time even to reach the Oort cloud.
https://en.wikipedia.org/wiki/Kuiper_belt
Everyone* knows about the Kuiper Belt, of course, but we are looking into at least two other “reservoirs” of TNOs between those named ones.