Why did they change to kgs ? Who knows but it was probably someone in MOD who decided as a 'pet' project. I too had left before the change. During the build up to GW1 (a busy time for all) MOD scored the own goal of insisting that all cargo etc for the 'K' was to be in kgs. This caused the inevitable problems as well as adding to an already overburdened system.
I phoned the chap in MOD who was responsible for this. He said it had been planned for a long time. I suggested that this sort of nonsense was not what we needed at this time and a postponement might be in order. Not a chance was the reply.