Barn find motorbikes are undoubtedly cool, but they’re even more amazing when they can actually start with minimal fiddling necessary. You need spark and compression, of course—as well as fuel and air. The longer a bike sits unridden, the greater the chance that the fuel system (particularly if it’s carbureted) will be clogged up. A flat battery is a relatively easy fix, but some problems require deeper investigation to diagnose and repair.
For those reasons and more, barn find “will they start?” videos are almost always fun to see. Just because a bike looks great on the outside doesn’t mean that it will start—and just because it looks terrible on the outside doesn’t mean that it won’t start, you know?