Being harder is a GOOD reason to do it on water
If you can make it work reliably on water when the station keeping isn't necessarily exact and the waves will move the platform up and down to some extent, it adds an extra level of assurance that doing it on land will be problem free.
Still, hopefully when it is done on land that is very near a large body of water, or at least an uninhabited area like a desert, so there's a convenient place to abort to if problems are encountered on the descent.
Biting the hand that feeds IT
