DMU is a great excursion vehicle, btw. It will run on any kind of track. They can get into harbors, industrial sidings and recently closed sections where mainline loading gauge equipment has no business to be in.
What's more, the railway operators weren't so skittish about their monopolies (they had a legal monopolies back then), so many were just given to preservationist associations. Now everything goes to scrap with strict no reselling contracts.