Country roads also have a) considerably less traffic and pedestrians b) often have obvious blind spots which drivers cannot speed around without very obviously rolling the dice. Its why you see traffic calming measures in Belgium and the Netherlands which are in the form of straight avenues having lots of bends[0] in to ensure drivers have to pay much closer attention to the road.

Further to that, putting signage on a lot of these rural areas isnt economically viable for a road that has very little thoroughfare and associated accidents. That said, having 60 everywhere and trusting drivers sound insane

[0] https://www.youthforroadsafety.org/news-blog/news-blog-item/...