Seatposts were very hard to come by back then, barely measuring 100mm in most cases, so frame manufacturers had no choice other than to extend frame tubes
I can honestly say that I've never been to a trail centre to make use of the 'groomed' trails that they offer. It just doesn't appeal. Never has, never will. Give me a rough and ready bridleway over a moor, or an old drover's road between two dry stone walls, and I'll be happy.