I'm not talking about paying for grader notes. I'm disagreeing with your assertion that CGC customers need to know how to grade.
I pay CGC for a grading service. Whether I know how to grade, has no bearing on the level of the service they provide.
If I hire a vendor to build a website, whether I could do it myself is also irrelevant. I am hiring someone to do it so I don't have to. If I know how to build a website myself, it may put me in a better position to evaluate whether they did a good job, but that has no bearing on the level of service the vendor provides.
For me, it add value to their service if they included notes for all books. I'm not saying it's a dealbreaker. However, even if I am an okay grader, it is useful to have the 2nd opinion. Notes are also helpful if I want to sell the comic. Indeed, I would consider paying extra for grader notes on every submission as an upgrade (like imaging). I'm sure CGC would love the opportunity to extract more money from their customers. I'm assuming it would take little effort on their part to include the notes, but maybe it's more difficult than I think.