That is because it doesn’t make sense to do so, all the configuration related to the dataset (the columns, data returned, filter criteria, etc) would be different and you would need to start again anyway?
Not always. But perfectly understand your opinion.
I had some situations, usually when exporting layouts between CMS or within the same CMS that this feature would help.
Example: I made a layout in a dataset. I just created the same dataset in another CMS. Export the layout for the new CMS and can not use, I have to delete the item from the timeline and copy in hand.
Sure, that is a good use-case. We’ve addressed that for 1.8 already so that the layout export includes the dataset structure (and optionally data), which can be recreated or matched to an existing dataset on import.