"Why do we bother fixing up our old vehicles?"
Why does someone go golfing? Read? Do carpentry? Collect stamps? Watch sports?
Because it's called a pastime or hobby and we like it, that's why!
Personally, I take a great interest in many aspects of restoring an old vehicle.
The hunt for parts and pieces is fun. Learning about old technology and engineering is an interest. Taking something that is totally messed up and making it new again is satisfying. Preserving historically important artifacts is a service to the public.....

Nothing ticks me off more than when people ask "what are you going to do with that old thing?"