They lost control, whereas a ditching, to my mind, is a controlled alighting or landing on the water, which is not such a shock. This helicopter hit hard, and pieces came off everywhere, as we know. That's one aspect of it.
The difficulty is that helicopters in oceans usually turn over, and they turn over very rapidly, so a lot of training goes into survival, because if you are not trained in getting out of the helicopter, you're going to drown. If you have gone through the training--especially if you're physically fit, mentally strong, don't panic, know what to do, and have a plan as the ditching begins to take place--you have a much better chance of getting out of the helicopter.
To the best of my knowledge, most people involved in helicopter crashes are not killed in the crash. They drown. However, if they don't drown, they face a further ordeal, especially in our very hostile waters.