Hi,
If you enable the comments in the previously indicated section in the configuration, so that should be displayed on all the views.
In your case, if you have enabled it, so you have potentially an override on the view "product / show_default" and in this override the comment part has been removed.
Please backup your view, and reset it by clicking on the dustbin in the views listing via the menu Display > Views.
If you don't have overrides, please give us a screenshot of your comment settings in the configuration.