I've worked on a few neglected bikes recently, well in fact all on them have been. I've begun to see how they got to where they are.
On the gold wing the starter had issues, I found a trail of double nutted studs and loose bolts leading to the starter removal. Someone just gave up before actually fixing the starter. The inside bearing was bad.
The rear brake pedal was rusted solid at the pivot, the entire bike was very clean however so I'm guessing it was injected with car wash water. I fixed that but when I tried to bleed the brakes I noticed the rear bleeder had been removed and lost. Another job he didn't complete. Way better than broken off as I feared.
My 750 K0's engine was gas stained, the carb bowls looked like the tar pits and the petcock was frozen. Apparently the gas had been left on until all of it leaked through the carbs. It had to have been stored in an outside shed.
The low mile Yamaha, the starter and relay was toast, and the carbs were plugged up but the battery was new. He apparently wore out the starter trying to start it.
The drag bike was missing all if it's small and easy to remove hardware, clutch and brake parts, throttle tube, grips, it lived in the back of a bike shop and was fair game for small parts removal.
A guy was looking at my 750 sandcast recently and said he had rented a house from the original owner. The sandy was in the shed, he could have bought it for $200. Didn't want to spend the money to get it running.
Someone just stopped caring enough to fix a few small things and that begins a spiral of neglect until I buy it cheap and undo all of that.