If it's not verifiable, there's a great deal less value in referencing it. Arguments over facts can simply shift into arguments over the meaning of the Giant's comments on those facts.
Which is valuable in and of itself. And this criticism applies to everything in the index.

The more comments that are in the Index, the more unwieldy the Index is to use; intentionally adding comments with the expectation that they have no worth on their own seems counterproductive.
That's certainly not my intent. As best I can tell, it's no one's intent here (those who think it valueless on its own don't want it included, whereas I think it does have value on its own, and more in collection with other similar quotes).