Here's why. Every individual has two commodities they own:
People with #2 tend not to have #1, and vice versa.
So for someone with a good income, it's just not worth the time involved to locate a torrent, download it from the few people seeding it, etc., etc. (Even if YOU could find it quickly, there's still a learning curve involved for the average person.)
The people who pirate software almost always are those who wouldn't buy it in the first place, simply because they don't have any money. But by getting your software, a certain tiny percentage will help you via word of mouth, which in the end helps your bottom line.