I'm guessing most of their money comes from businesses who purchase licenses for their developers. I've personally been responsible for four license purchases (my own + 3 companies bought a license for my work computer).
Then you don't own a license, the business does, and they can re-use it for any employee, as long as only one employee gets a license at a time. Their FAQ explains it all well: https://www.sublimetext.com/sales_faq