Bitcoin is only popular because of its price and only in the internet. USD is popular all over the world and use even in public conveniently. They have their own purposes, let's just say that bitcoin can do something and USD can't and vice versa.
That is right. However, when the bitcoin becomes more widely used, people will prefer bitcoin in the future.
You are very much right. USD is being used all over the world since very long period of time. On the other hand BTC was introduced only 8 years ago. I think the way Bitcoin is getting popularity amongst the people; it is very much possible that it will beat the USD in the race. I think at that time, things will be very much different than now.