Did $100M investment help Github to win, or had Github already won in 2012 with profitability and 3M git repos?

I would argue that GitHub already won in 2012. The investment helped us grow in a different way, but I don't think anyone involved in that deal would have said that we had almost any serious competitive threats at the time, which is to some degree why it was such a great deal.

Did the investment encourage corporate buyers to sign up for Github Enterprise, where corp developers were already using the free product?

That was certainly one of our internal arguments, that the institutional investment would be helpful for large company trust.