It isn't really a moat so much as a loss leader. Travis CI was free back in the day IIRC.

So it's a moat that trickles out to the sea and has to be kept filled very expensively.

(I'm just keeping the metaphor alive because for me it is the primary blocker, whatever we call it.)

Well if/when GH eliminates the free tier, I'll probably churn. I agree that's the main thing keeping me there.