I've thought about why open-source software projects often run short of non-technical contributions. The factors I suspect:
1. The non-technical roles in a software project are less autonomous. A programmer's pull request for a new feature is likely to be seen positively and accepted. A designer's logo is likely to inspire non-designer's to share their opinions and aesthetic preferences.
2. The work is less creative. Coding up a new feature or quashing a bug can be an epic adventure. Writing a tutorial on an existing API less so.
3. Open source software tends toward directly solving the problems of programmers. ZeroMQ, Jquery, Capistrano, Bootstrap, etc. don't create economic value for community managers.
4. In any given market, programmers are likely to be better compensated than non-technical people. In light of where the economic benefits of open source software tend to accrue, there's a sense in which seeking non-technical contributions is a bit like welfare for the rich.
The question posits one benefit: a non-technical person might be inspired to learn to code. Wouldn't such a person's time be better spent learning to code instead? Wouldn't their time be better spent doing paid work in an environment that might just as well inspire them to learn to code?
Makes me wonder which open source projects are paying non-technical contributors?