When you upload a file from your computer to ArcGIS Online, if you share it with Everyone, you see a link to the file in the item details. If you don't share the file with Everyone, even if you share it with a Group in your organization, the url link in the item details page goes away. Is this by design? I found this help page:
which states: "You need to share the CSV and image files with everyone (public) to see the URL in the item details page."
In my case I'm sharing a pdf but I do see this behavior. The question is why? Maybe Esri doesn't want people using AGOL as a file repository?
This is an interesting question. I guess it would make sense that you can see the URL once the service is public (same goes for files). And you're probably right about the data repository thing too. Though, I can see links to 'services' that are only shared in my organization and cannot see them publicly.