If your refferring to the Beaver that is operated by Sea King airway then it is a monetary based thing.
A few months ago I was wandering around on the tarmac and he happens to park just accross on the other side of the taxiway from our aircraft.
He went through all the financials of why flying no final leg saves them a few minutes in the circuit... but in the end you would be amazed it actually saves them $12000 a year in fuel savings. It costs 1200 an hour to run.
PM me if you want the finer details.
M/E