Because BTC is strong when people are aware from that specific country, for example, Japan is a good example why BTC is strong there, its because that the citizens around Japan are very much aware and are knowledgeable about BTC and that is why BTC is strong in some countries that has an uprising economy.
This is an open secret because all those who invested in Bitcoin initially in the start were majority from America and this is why the largest number of investors in Bitcoin is from US. So this is the reason because they had financial resources.
Yes, it is evident. Their salaries are high, and they are also more open to everything new. People that live in the counties with good economy feel that they are financially protected.