No, its not for the UX, but for tracking you in every way as precise as possible.
Second, most of you is not Facebook or Google either and have no need for additional complexity.
Third, a strategy some of the big companies do to slow down startups that may compete with them is to create an illusion of how fantastic it is to develop applications with this new tool. So instead of focusing on actual business value, a lot of people spend time on premature optimizations and think API's that are breaking daily is perfectly fine as their favorite tool is only getting better.
Second, most of you is not Facebook or Google either and have no need for additional complexity.
Third, a strategy some of the big companies do to slow down startups that may compete with them is to create an illusion of how fantastic it is to develop applications with this new tool. So instead of focusing on actual business value, a lot of people spend time on premature optimizations and think API's that are breaking daily is perfectly fine as their favorite tool is only getting better.