Inside the article, all source code is posted as images using Carbon. That way, your readers can follow along and understand what you're doing.
But you didn't have to give away the source code, so you can still ask people to sign up for your $5 monthly membership which grants access to all source code projects as downloads.
Of course, your dear readers could also manually type in all the source code shown in the Carbon images, but at that point lazyness kicks in and they pay the $5.
My personal opinion is that knowledge should be shared, so I'm not sure if I consider such an approach good for our craft. But I can understand the business model that is created by having a tool such as this, which allows indie developers to earn a passive income from tutorials.
The next logical iteration is then to put your source code screenshots into a video, e.g. https://gorails.com/