And GitHub rankings don't factor in things like the fact that java programmers may be under represented, because they tend to be older with enough experience and contacts to get work - without needing to show a GitHub project (plus if they have kids, they just don't have the time)
I'm in my 30's and one of the younger people in my department. I work in Engineering. I don't use Github I do not know anyone personally who uses it. I think it is probably a generational thing.
Search engine result as well I'd be suspicious of. If I am searching a programming language it is something I don't use very often thus why I am looking up the information. The languages I use the most often I have stack of books on my desk rarely need to look anything up with a search engine.