Bieszczady Mts are special. Quite remote (in a "corner" of all three aforementioned countries). Still, there used to be numerous villages and pastoral steads. The WWII changed everything. Borders shifted, most of the inhabitants were forced do leave and settle elsewhere and then neither of the three countries was interested in re-populating that region. Then, as the communist govs became more relaxed, people started moving in, attracted by the pristine nature and sparse population. But with time Bieszczady became so popular that it's quite hard nowadays to walk alone there. The trick is - the crowds will always go to the most popular place (like the highest peak, a a viewpoint etc) and to places easily accessible. I am not in either group and that's the secret to enjoying hiking without crowds.