Most bitcoin users come from good economic countries because this countries are abundant with power supply and a strong internet connections, that is why they can rely on their uninterrupted supply which strongly needed in involving cryptocurrency activities and works.
I think since the country's economic it was good, the population can buy everything needed to buy a tool that made the means to manage bitcoin. for example the necessary tools is PC or Internet network. and I think since most of the population in developed countries already have access the Internet and electronic equipment. and technology education in the country existing and the majority of people want to learn to use technology.