WHY INTERVIEWS!

What is the purpose of interviews? Why reduce all the knowledge one has into a 20 minutes or 30 minutes sitting to determine whether he qualifies for a job?
I  understand it provide an avenue where someone's papers can be scrutinized but being asked a lot of questions to gauge one's performance is not right.Answering an impromptu question doesn't mean you can perform, in fact it encourages cramming which is an hindrance to performance.
Society need to invent a new method of gauging performance other than the archaic method- interviews.
I suggest people to just present their papers, panel to look for qualifications and allow the qualified to work. Performance need time to gauge and interviews provide no time for that.
Some may say people acquire certificates through underhand methods and therefore the suggested method is not right; My question is- how different is that from cramming a whole booklet and pour it out on an interview only to remain with nothing to offer in service?
Society need to change in every aspect, some norms we  can't  continue  transferring
from one millennium to the other.