And its not the done thing in any of the operations I have seen (but always refuse to get on) to put life jackets on before departure over water.
Well, I'm just a PPL so I wouldn't know how this is commonly done in commercial operations. (I haven't even been passenger on a commercial single-engine overwater flight.).
I can only say I am very surprised that you say it is not done as the greatest danger when ditching is not surviving the ditching itself, but surviving in the water until SAR reaches you.