That's the difference.
What threshold must you cross (in terms of platform size) for silence to equal complicity? Since it apparently doesn't apply to you, but it does apply to a GitHub repo.
Once you've made up your imaginary platform size threshold, which movements must people not be silent on, lest they find themselves complicit through silence? Is it ALL political movements? Those READMEs are gonna get pretty long if so. Is it only the "most important political issue at the moment" that needs to be voiced? Who decides what the most pressing issue is? Is there some sort of vote going on that I don't know about? When is it OK to start being silent again? If he puts up a BLM message in his repo and then takes it down the next day, is that OK? Or does he need to keep it in there forever (because presumably Black Lives always Matter, so he should keep it in there indefinitely, right?)
There are way, way too many things going on for silence to mean complicity.
Take any other humanitarian crisis, and ask yourself if anyone silent must be complicit. Think about it for a second. It's just not true. If someone in Germany were to not speak out against the Nazis rounding up Jews, but at the same time was hiding Jews in their basement, would that person be "complicit" in the Nazis crimes?