The cost is minimal. There's a reason why it's still free on PC. Additionally, you could offer a free option by letting users host their own servers, but that would go against the walled garden bullshit that lets them charge so much for such a cheap service. In fact, I don't know if it's changed since the earlier days, but many console games had games hosted on user consoles anyway, it's just the initial matchmaking which uses the company's servers.