Bitcoin is not as popular as the US Dollar. US Dollar has been there for a long time so people have talked about it ever since. Before most of us were born, people already know about US Dollar and it has more value than most currencies.
Bitcoin, on the other hand, is relatively new. As we approach a more and more digital world, Bitcoin is also arising. People are starting to talk about Bitcoin but I don't think it will come to the point that Bitcoin is more popular than US Dollars any time soon. But it will, eventually.
Yes, bitcoin replacing or becoming more popular than us dollar is for sure, but that may not be very soon it may take some time to reach that stage because it is still unknown by many people around the world, most especially people frm the developing or under developed countries.