Data is impossible to read - seems like some people are converting their salary to USD, some others leave it in their home currency and a rare few provide the accurate currency. Interesting initiative though - would love to see this in a better format :)
I am European and live in Europe but I've always been paid in USD and my salary is negotiated in USD, so I am not sure what parent means or why does currency matter.
First clients were based in the US. So it started from there.
Then I wanted to use a reserve currency[1] and I happen to have strong opinions on currencies, policies (FED, ECB, etc.), so I opted for the safest bet in the long run.