You can add airlines to that list. Here's[1] an article that goes into it a bit. American Airlines actually loses money on their whole "flying people around" business. All of their profit last year was derived via selling points/miles for their frequent flyer program. And it's not limited just to American - I'm not sure about foreign carriers, but it's really common for US legacy carriers to derive substantially all of their profit from marketing revenue related to their loyalty program.

[1] https://viewfromthewing.boardingarea.com/2019/01/24/earnings...