I don't work for DO so I could be wrong, but it's my understanding that they actually pay the community for contributed articles to their knowledge base and tutorials section. This is a brilliant idea (if true).
Probably really great SEO/marketing value, and quite useful content. Example being annoying stuff like manually configuring an OpenVPN server + clients, DO seems to have 2 out of the top 3 Google results.
Looks like Linode started a similar program at some point: https://www.linode.com/docs/linode-writers-guide/