Yesterday, I only had to worry about storing my data on GitHub if I was in direct competition with them on the integrated SCM business. Any other code wasn't in opposition to their interests. We, generally, were welcome.

Today my code on GitHub is in competition with the myriad projects that Microsoft publishes. And even if I stick with Windows coding, they too can and will incorporate it into their stack.

Tl;Dr. Doing stuff on GitHub is directly competing with Microsoft's own business.