A key feature of space is that it's relatively empty. Especially as you get farther out.

While the Voyagers don'tt have detectors for dust impacts, I did find this from New Horizons:

> the Venetia Burney Student Dust Counter only counted a single dust particle within five days of the [Pluto] flyby. This is similar to the density of dust particles in free space in the outer solar system — about 6 particles per cubic mile

https://www.nasa.gov/feature/top-new-horizons-findings-reported-in-science/