Internet hasn't reached more remote locations till date, through solar power generators electricity is being used by people over those localities. This way it isn't that easy to reach a massive use of bitcoin among the common people. The growth over the under developed world is possible only if the acting government takes steps forward.
I think that figure is quite enough to keep cryptocurrency functioning well, as I speak, ever since gsm has been introduced, we still have some remote part of some cities of the world that are yet to even know what those gsm is all about, but that still has not stopped the gsm from functioning well, so same way that bitcoin technology can grow very high without those people and maybe get to them with time.