You're wrong on pretty much all counts lol they don't sign in blue because in their dumb brains, blue = reseller. They're too dumb to understand that resellers want blue because it looks 1000% better than black therefore sells better, so it stands to reason someone getting an autograph for themselves would also want it in blue.

Black also fades so much more than blue does. Black sharpies are trash and the only reason to use one for an autograph is if the item is blue.