Modern HE machines hold much larger loads than traditional front loaders which had a maximum capacity of 8 pounds or so. Even if the modern machines were not rated for larger loads, owners were going to cram as much as they could into those large drums, because now doing laundry is just such a back breaking, onerous burden on anyone who has to do laundry today.
There could always be the situation of water heaters being turned down so that they do not provide the traditional temperatures associated with hot water in decades past. With more people using cold water, whether by choice or by the machine using so little water that even if hot water were delivered to the machine, there is not enough thermal energy in the water to warm up the machine, detergent manufacturers might be trying to cover their asses with cleaning issues by recommending greater detergent dosing. Remember you have mechanical action, chemical action and thermal action that go into successful laundering. If you are low on one, you have to increase something else.
When I wash a load of 5 bath sheets in the Speed Queen, I have to use double the regular amount of STPP and detergent over the amount I use for regular loads because it takes a huge amount of water to saturate the load. A beneficial side effect of this is that all of that hot water really heats up the load and the machine so things get a good hot wash. I always bleed the hot water to maximum temp before starting hot wash loads.
