Mobile operators claiming that the vast majority of their subscribers use less than 500 MB of data per month are talking differently in public than in a recent survey, in which most operators say they expect a 20 fold rise over the next 5 years. Just do the math on watching YouTube at a 1 Mb/s bit rate: you would burn through your monthly allowance in just one hour. 500 MB is really just nothing.
So, if these operator claims about users staying below the 500 MB threshold are right after all, then there are two possibilities:
Subscribers aren't using mobile data's full potential.