I think one of the reasons why is because some people just don't like change. Changing from Windows Xp to Windows 7, 8 or 10 will just be difficult and they just choose not to adapt. The interesting thing is that Microsoft on April 8, 2014 officially ended support for XP and according TechRadar back in April Windows XP is still the third most popular OS two years after end-of-life. Maybe those who still use it just like how it runs and performs.