When you are a multi-million motorcycle factory you can't think about the things you make with your heart but with your head. The price of storing parts for decades is outrageous, far bigger than the part price whatever it may be. In fact Honda shouldn't even have to had any warehouse for parts; if they are applying the "Just in time" policy the japanese factories are so good at, they would just order parts from their manufacturers as soon as they receive an order.
Those dealers who bought the parts 40 years ago and will have them re-bought by Honda had lost lots of money. They paid market price back then and are getting market price today. The only thing they have been able to achieve is to keep up with the cost of living. But had they invested the money in other thing, they would have much more money today. Not to speak about the cost of having and maintaining a big warehouse, and the opportunity cost.
You have to change your mind: these old bikes, even when we love them, are just old pieces of machinery. Industry can build far better bikes today, at far less cost. That is an improvement. Keeping old bikes on the road is not reasonable from an economic point of view. Thanks God we still have quite a few spare parts around. Let's enjoy our bikes while spares last!
Can you imagine Kodak re-buying all their photo films? It is all gone now, its time went by such as typewriters, walkmans and tube tv.