It wasn't a good idea to use shortened links in a citation in the first place, and somebody should have explained that to the authors. They didn't publish a book or write an academic paper in a vacuum - somebody around them should have known better and said something.
And really it's not much different than anything else online - it can disappear on a whim. How many of those shortened links even go to valid pages any more?
And no company is going to maintain a "free" service forever. It's easy to say, "It's only ...", but you're not the one doing the work or paying for it.