The reason is that it may only have 10,000 miles on the engine but it is over 30 years old.
the rubber parts especially the cam chain guides and rollers can come all apart
and the bits of rubber get in the oil pump.
One person got a old CB750 and found out the back brake shoes
had come unglued from the backing plates.
Also piston rings can get jammed from corrosion because moisture
can get in the engine. Unless they plug up the exhaust and the intakes.
I have never seen a bike sitting in a garage or outside of a building
with plastic over the exhaust.
Electrical connectors corroded beyond repair.
On a Roadstar Adventure.