Because of the scattered landscape that is linux, they don't have any comprehensive forum or proper handbook like FreeBSD does - so yes, sites like stack overflow are one of the many rescue centers they go to. Why would anyone using FreeBSD want to deal with the toxic ecosystem on stack overflow (purely oriented towards reputation and competition) if you have this forum that is even directly linked from the main project site?
As for such "competitions" and statistics: I couldn't care less. I don't use FreeBSD (or any BSD or illumos) because of its popularity, but because of its stability, professional ecosystem/communities and sanity. If I want to constantly fight the OS to do what I want I could just use that advertising-platform from Redmont.
