Imagine you invest in a bond that is barely investment grade with a credit rating of BBB-. Then, a year later, the credit rating agency comes to you and tells you “Remember the bond we told you last year was investment grade? Turns out it was junk-rated at BB+ already back then.” How would you feel about that? If you’d be mad at them, then you should be mad at some ESG rating agencies as well.
Let's make it up as we go along.