They're largely living off money from past films. Residuals help, but it's mostly the paychecks. Screenwriting is somewhat unusual, though, in that the officia

They're largely living off money from past films. Residuals help, but it's mostly the paychecks. Screenwriting is somewhat unusual, though, in that the official credits for a film don't always represent every writer who got paid for the project. There's a whole complicated thing with establishing who gets credit and who doesn't. Union arbitration can be involved, and so on. There's often a lot of intermediate drafts that don't lead to credit but nonetheless earn big paychecks for the writers. And of course writers are often paid for scripts that never get made at all. The big win is writing a huge hit that earns substantial residuals for years, but there's a lot of money made at levels below that too. As for who is footing that bill, it's the producers/studios.