Keep in mind that the essential point of research is to copy. People cannot establish the result based all on his/her own contribution. Innovation is to develop something INITIAL, hence people need to know what has been studied previously.
PhD is the abbreviation of Doctor of Philosophy. Doctor originates from a Latin verb, docēre, ‘to Teach’, and Philosophy is originated from Greek, ‘to Love Wisdom’. Hence a PhD is a person who is able to investigate the reality and principle from nature based on logical reasoning.
To pursue a PhD degree is not to refer to the academic advisor for the details of the research, but to learn the method, and cultivate the capability to know how to initialize and create a direction independently. The research could be left out forever once completed.