How much work is it really to keep goo.gl links around?
A lot.
Goo.gl has a namespace for 10 billion entries, it used to keep tracking/analytics data for each link, with a user interface, and it would happily generate them for links to internal stuff.
Just keeping it running would take some containers of server racks, plus updating the security, accounting for changing web standards, and so on.
Keep in mind this isn’t some self-hosted url shortener with less than a million entries and a peak of 10K users/second, that you can slap onto a random sever and keep it going. It’s a multiple orders of magnitude larger beast, requiring a multi-server architecture just to keep the database, plus more of the same for the analytics, admin interface… and users will expect it to return a result in a fraction of a second, worldwide.