A lot of mentioned software was started many years ago, when other languages were hardly viable options. And those programs are good enough now, so there's no much movement to replace them. It's not a good argument for C, IMO. It's like telling that Windows is awesome because so many users use it. But when people started from scratch (mobile world), it turned out, that Windows is not the best OS.

Actually when I'm reading about new software, it's very rare to encounter C. Usually it's something else.