I think I'm not getting what your post clear because what I see is not every writer can make a passive income. Passive income means you have done the work already and your now benefiting from the work through the income of the work done. I hope I'm clear here, OK let me still break it onto feather piece.
let's take a farmer who grows a biannual cash crop like cocoa, coconut, cashew and other things. All these crops will give the farmer passive income because he will continue yo earn money from those crops.
Another way to earn passive income offline is from real estate development. If you are able to establish let's say one or two hotels or build school or even apartments for rents, you are going to receive a passive income but as I already said these are the offline ways. Writers earn passive income mainly on writing new books and selling them online. Some writer can also write article and earn passive income from them but if you are a writer and you are only commission yo write then see to it that you will never earn any passive income from that although you are still a writer.