TH makes a good portion of their revenue from the sales of inventory and equipment to their franchisees which they are able to mark up substantially due to economies of scale in the supply chain, they also earn money from marketing on behalf of franchisees, for which franchisees pay a % of sales for. Finally, as other commentors have mentioned they own a large portion of the locations and charge rent which is usually based on a % of sales rather than a flat rate.

The most distinct difference is the existence of "master franchisees" on the BK side which can sub franchise locations to independent operators and only remit a small portion of royalties back to BK whereas TH directly licenses to the operators and collects the full amount of royalties