There were a lot of hardships on the sea and at the time often 40% of the crew died on the single cruise. Diseases, storms and malnutrition were the main problems for both pirate and legal ships.
Actually the Pirates rarely sunk and burned the ships. Most of them let the crews of the captured ships continue their journey with most of their supplies. That let the stories circulate that it paid of more to surrender to the pirates than to oppose them. Hornigold, Bellamy and Blackbeard were particularly known famous for such behavior.
Thanks for the insightful comment! :D