Maybe Pirates are interesting because the subject isn't used that
much for the most part? I mean, fantasy and vampire stuff have all
but been driven into the ground with a mallet, to the point that its
really hard to add anything new to it.
But pirate and swashbuckling stuff is still fairly uncharted
territory, and I mean stories that actually really deals with
pirates from their point of view, not just sea voyage stories like
Master and Commander. I can't hardly think of any Pirate movies
besides the Johnny Deep stuff. (Well, I guess Princess Bride
counts. Sort of)
The only pirate anime I know of that's pretty well known is One
I think the other reason we like pirates is because they are often
the reluctant hero types, which is usually pretty interesting to
watch. This is all off the top of my head, I don't think its
terribly cohesive. I'm way behind on posts too...
Mills-"May the Lord smile."
Garcian-"And the Devil have mercy."