Who is making big money JUST off novels? Not speaking, not tv deals, writing.
Meanwhile I know several game developers making a living. Setting out to do it still follows a success distribution, but it’s fundementally achievable in a way unavailable to writers entirely.
Seems like urban supernatural or romance (or urban supernatural romance) seems to be the main genres where this is working. My girlfriend follows several writers who make a living this way, and is wanting to give it a try herself, that's how I'm aware of it.
You can't write The Great American Novel or spend years writing your novel and make money this way though. It pretty much requires the momentum and consistent quick releases for it to work. You're making sugary garbage that's consumed quickly and forgotten just as quickly.