Most of it.
For me it's waaay more fun than riding busy paved roads especially after getting hit by a car last year. While it might sound a bit cheesy I also like being closer to nature.
We don't have maintained gravel roads here either that get used by passenger vehicles, mostly just dirt roads that hunters and farmers use with tractors and 4x4s. But I barely meet anyone.
I get to ride quiet, calm roads while looking at nice scenery. Win-win.