Goo.gl was a terrible idea in the first place because it lends Google's apparent legitimacy (in the eyes of the average "noob") to unmoderated content that could be malicious. That's probably why they at least stopped allowing new ones to be made. By allowing old ones, they can't rule out the Google brand being used to scam and phish.

e.g. Imagine SMS or email saying "We've received your request to delete your Google account effective (insert 1 hour's time). To cancel your request, just click here and log into your account: https://goo.gl/ASDFjkl

This was a very popular strategy for phishing and it's still possible if you can find old links that go to hosts that are NXDOMAIN and unregistered, of which there are no doubt millions.