What I think is key for open source is the quality of internet access we have these days. You can copy any repo without really thinking about it.
The other aspect is that open source is extremely mainstream. Mobile is still a reflection of the old world where everybody tries to make a small amount of money which some closed source apps.
Lots of people realize that is it is better to collaborate with other people in an open source project then to be on your own writing your own programs.
All of that would work just as well on SVN.
Ditto with Python.
Ditto with pretty much everything computer related.
It's as if the extensive shift in education starting in the 1980s or so, to emphasize training with computers and programming, has lead to a large number of well-trained, competent programmers.
I think it's pretty clear, though, that both the quantity and quality of open source software has increased drastically in the last decade or so. I think it's fair to say I may have stretched the degree of causation git had, as opposed to just correlation. But I also think it's pretty evident git, as a tool, had something to do with it.