Maybe because of it's unstable exchange rate 
i disagree with you and i think you already know that bitcoin prices has reached the lowest prices in 2015 but people still use bitcoin and my guess is if people would stopping from using bitcoin because bitcoin will banned for all countries i think this is the main factor Unstable exchange rate can't be accepted as a issue with Bitcoin. Its the nature of the running technology behind Bitcoin. I believe more people are into Bitcoin due to its unstable price.