Why are authors not made anonymous during the review process? During the review process of an article, the reviewers are (almost always) anonymous by default for obvious reasons.

Why are not authors also made anonymous?

It could help remove the weight that established authors carry in certain fields (which can tilt the scale in their favor), as well as the stigma associated to research coming from non-developed countries.

Are there any good reasons why this is not done? I can not think of any.
Sometimes they are. That's called double blind refereeing. It is becoming more common.

From https://www.maa.org/press/periodicals/guide-for-referees


  The Board of Governors of the Mathematical Association of America has
  mandated that our journals use a double‐blind review system.


This blog post and comments discuss the history, pros and cons of double blind refereeing in  parts of mathematics and computer science.