Also, in quite a few houses, the initial run of water out of the hot tap is cold for quite some time until the hot water has either made it round from the hot tank, or if you have a combi boiler system then after that has fired itself up, got up to temperature, and then the hot water has made it round the pipes from there. It may be that the washing machine uses so little water that most of the water it gets from the hot supply is cold, wasting all that energy.