Question

Whys gross domestic policy not necessarily an accurate measure of a nations standard of living

Answer 1

GPA is not a good measure of a nations standard of living because it does not include transactions where money is not exchanged in hands.

For example, GPA includes buying a meal at a restaurant but does not include making a similar meal at home.
It includes farmers growing and selling crops, but not people having gardens in their backyard. 

I hope this helps!