Yep, it sure is surprising to me too. I’ve only replaced one 8 inch section of the fuel lines in all these years.
I was surprised to find flexible plastic line too. It is quite a long section, the fuel supply line most of the way from the main tank to the tank switching valve is plastic. Sort of a hard but flexible plastic. It’s getting a little too soft in places as you might expect. Maybe it is actually rubber but 47 years have turned it into plastic 
When I was fiddling with the fuel lines the other day I noticed the plastic line developed a kink just by me repositioning it for a look-see, which is one reason why I’m thinking to replace it all. The fuel return line is mostly metal for some reason, smaller diameter.