I think the problem is that there is less often something to be said if you agree. Every now and then you might have something to add that fleshes out the idea or adds additional context, but generally if I totally agree with a comment I just upvote it.
On the other hand, when you disagree with something your response will, by logical necessity, be different from the parent comment.
So if you want to prioritize “adding something novel” there’s a logical bias towards comments that disagree since only some percentage of agreement will tick that box.
Otherwise you end up with a bunch of comments that literally or figuratively add up to “this”.
I think it depends on the project. Some projects are the author’s personal tools that they’ve put online in the off-chance it will be useful to others, not projects they are really trying to promote.
I don’t think we should expect that authors of repos go too out of their way in those cases as the alternative would just be not to publish them at all.