Just came back from a short trip to DE and AT yesterday.
Here in NL many of former quite long )in time, often not that much in distance) are-were split, as they went in 2 concession areas. There was a line via all new dams and dykes in the Zeeland area from Spijkenisse, end of metro to Midelburg/Vlissingen, serving only quite necessary villages and areas off the trainlines.
In DE there certainly are many more longer buslines, esp in the hilly-mountainous areas in the south, were rail is of course sparse. Check RVO°Oberbayernbus, which has-had a line, but just 1/2 times daily, connecting most of all those southern railends.
In AT I rode in a splendid Setra doubledeck coach-bus 950X from Lienz in transito via italy to Innsbruck, all the way parralleling trains, single is 17,50, which is oin fact the MAX single anywhere in Tirol, but I used a 7day all Tirol pass for bus and train for just 45eur.
Anohter reason ti split them is the ever stricter rules on driver/work/hours.
HU with the old Volan also has a lot of buslines of 5/6 hrs linking direct towns were rail would be the long way round.