Not an expert on this, but I'd assume one thing is that in 3-2-3 two people need to stand up and give way if the person in the window seat wants to stretch their legs or go to the toilet. 2-4-2 only one person has to get out of the way in all situations. Would guess that's actually somewhat important in widebodies since those are used on longer routes, and having to stand up twice as often in the aisle seat would be something of an inconvenience.
There's probably more, I'd guess that would also affect boarding times and so on, but this is the first thing that comes to mind.
Just in case someone misreads this, add the vinegar as the softener, so it's not in the first load that contains the detergent. The detergent is a base, and relies upon that fact to get rid of some of the stains, and vinegar as an acid will neutralize that. Vinegar is meant to be in the rinse cycle when washing laundry, where it can help get rid of any extra detergent by neutralizing it and do any other magic it does.
Also, though I don't usually encounter them often, do note that vinegar can wash away zinc and silver oxides used for some sterile clothing, and can supposedly damage lyocell.
But overall I second these suggestions. Most times the amounts listed for detergent are far too big, and you can often get by with less.