FCP isn't really making a profit for people who actually make use of their lifetime replacement services. I haven't purchased new wiper blades, brake pads, rotors, brake fluid, coolant, etc. in years. It's more of a long-term customer loyalty program. But for the average person who doesn't keep their car longer than 100k miles of ownership, it's unlikely they'll replace most other fluids and components more than once or twice within that ownership period.
My cost to return two 5 quart bottles and a filter has been ~$20. $20 is cheaper than buying two new 5 quart bottles of quality fully synthetic oil. Especially since I can get LiquiMoly from FCP.