What Were They Thinking?

I've got a long hatch the length of the cabin for bilge access.  It's about 2 feet wide and at least 12 feet long. I've got it completely opened up because I'm installing a new fuel tank. There's a place forward where the water lines run from the tank side of the boat to the galley side. The main plumbing is copper, but across this bilge opening they have inserted a section of rubber hose.

 

This is done very nicely by terminating the copper line with a flared fitting, then using a barbed hose adapter onto which the hose is clamped.

What I'd like to know, is why they didn't just slide the hose over the copper?