Enables in-place expansion of excerpts in the admin dashboard 'Comments' section of the 'Activity' widget to view full comments.
When you hover over the comment, a line of action links will appear (typically "Approve", "Reply", "Edit", "Spam", and "Trash"). If the comment has been automatically excerpted by WordPress, then a "Show more" link will appear. Click it to view the full comment.
The comment has not been been excerpted; you are already seeing the comment in its entirety so there is no need to be able to "show more".
Assuming you are using a supported version of WordPress, this just means that none of the comments being listed have been excerpted, thus there is no need to be able to "Expand all" or "Collapse all" in this instance.