I don't know the specifics of his case, but there could be several reasons. A likely one is that the benefits of a switch wouldn't outweigh the costs, at least

I don't know the specifics of his case, but there could be several reasons. A likely one is that the benefits of a switch wouldn't outweigh the costs, at least not within a reasonable timeframe. Another is that there may not be resources to dedicate to such an effort, even if the return would be suitable. And yet another could be management buying into all of the git hype we've been subjected to a lot lately. Git (and GitHub) today are like Ruby on Rails was a few years back. Even though there are several alternatives, some of them much better in some ways, they just don't get the media attention, and thus don't get hyped, and thus don't get onto the radar of managers who decide which VCS to use, and thus don't see as much use, and thus aren't even seen as viable options by said managers.