This week's business blog post explains why I make most of my resources (writing, open source software etc.) available for free. There are lots of reasons, but it boils down to low value payments across countries being a faff and I'm more likely to generate income from referrals / marketing (more people use my resources if they're free).
Of course, there is the risk that free resources aren't considered to have a value...
https://www.phpdeveloper.org.uk/why-i-make-my-resources-available-for-free/