The celebrity of Linus definitely helped Git win, and GitHub likely benefited from that by the name alone. Many people today mistakenly equate Git and GitHub, and since GH did such a good job of being a friendly interface to Git, to many people it _is_ Git. They did an early bet on Git alone, at a time when many of its competitors were supporting several VCSs. That early traction set the ball rolling, and now everyone developing in public pretty much has to be on it.
Tangentially: it's a pretty sad state of affairs when the most popular OSS hosting service is not only proprietary, but owned by the company who was historically at opposite ends of the OSS movement. A cynic might say that they're at the extend phase of "embrace, extend, extinguish". Though "extinguish" might not be necessary if it can be replaced by "profit" instead.
Tangentially: it's a pretty sad state of affairs when the most popular OSS hosting service is not only proprietary, but owned by the company who was historically at opposite ends of the OSS movement. A cynic might say that they're at the extend phase of "embrace, extend, extinguish". Though "extinguish" might not be necessary if it can be replaced by "profit" instead.