If you have been involved with backup and recovery for any length of time, you probably know two things: one, you should be doing DR tests, and two, you don't do them as often as you should (or ever, in some cases).
Why do they get performed so infrequently? Because they are painful. And I mean really painful. Try packing up 5000 tape cartridges, some of your top IT operations people, and a whole bunch of operations manuals and run books and heading off to a cold room without windows for three days of work. That would be 3 eighteen hour days, usually. Over a weekend. Not only is this not a whole lot of fun for anybody involved, but there are two other problems.