bitcoin is growing , people gets interested more and more everyday
why not bitcoin can be worldwide coin
Because not all of the people in the world can afford such coin, and, they are not tech savvy, they are just contented on what they have, and if you want to make these digital currency global, you need to wait for the bitcoin to be scaled.
Affordability is not an issue with Bitcoin, although the other points which you have posted may be applicable (such as technological knowledge). It is possible to purchase Bitcoin in extremely small amounts, such as
BTC0.01 or even
BTC0.001. That makes it possible for extremely poor people to invest in Bitcoin.