Depends on your market, it appears for me, most of Europe is Safari / Chrome, but Japan is almost entirely IE 11, China is mix of IE / 360 Browser. Sometimes it's not easy to not care.
Do you have a source for that (DeviceAtlas or similar)?
This is just observation based on stats from Google Analytics at work. I hope you're not assuming that my statement is the overall usage of browsers by country.
Depends on the size of the company and the userbase.
For us IE11 alone is over 3 million users a month. The size of a small country.