I assume this was off Indonesia. Indonesia is very corrupt. Having visited major cities in Sumatra such as Medan, there is not a lot of wealth. Add that to vanishing forests and a growing population, with little education, and lots of people are willing to take risks. In addition, I've read allegations previously that there is evidence that the Indonesian military supports the pirates, ie. they are actually working for corrupt military/political officials.

If you ever do ever visit Medan, check out the taxidermy museum, it's not the sort of thing I'd normally support but it's the most awesome such museum on the planet by a long shot (even better than Walter Rothschild's legacy at Tring in the UK).

Incidentally in the last few days they just had a major earthquake a hundred clicks offshore to the south of Sumatra, and reports of tsunami waves. The northern tip, Banda Aceh, was one of the worst affected locations in the huge tsunami a few years back. It's enough to make you head to the northern coast and try your luck as a pirate.