And, according to Wordnik:
It has to do with a literary tradition derived from Medieval Romances. To cite a dictionary in this instance is like saying the Ramones aren't punk rock because Merriam-Webster said the Sex Pistols are punk rock. You're cherry picking one of many meanings and missing the entire history.
To argue that pirates are not romantic figures is so far from my frame of reference that I don't even have the energy to connect the dots from Amadis of Gaul to Orlando Furioso to Dafoe to Byron to Robert Louis Stevenson to Sabatini to the Dread Pirate Roberts.