Total guess here: In addition to having two products that do the same thing, I'm guessing they may want to distance themselves from goo.gl links since a shortened URL with that domain somehow seems associated with Google and seems more legit (as opposed to, say, a bit.ly or ow.ly link.)
Interesting guess. Google does have a URL shortener for google "official" URLs under the g.co domain. And the goo.gl does get used for certain attacks sometimes.
