I think it is about control more than anything.
Some people have a personality that requires them to be in control.
Or maybe it is about being able to say they did it all and if helped they can't say that.
But let's be honest, everyone on this message board is old enough to know how to do a load of laundry. I can't think of a valid reason why a 20, 30, 40, 50, 60, 70, or 80 year old does not know how to do a load of laundry.
Will they do it the same way? No. Will they use the same amount of detergent or fabric softener, no. Will the different method ruin the clothes? Highly unlikely.
I think a lot of spouses also have convinced their spouses they are helpless and can't reliable perform household tasks as a method to keep from helping.
My wife and I decided that if we felt so strongly about a particular task being performed a particular way, it was our task and our task alone to do. At no point should we get upset we were not getting helped on the task because we had made it clear it had to be done our way or the highway. We actually have no tasks either of us feels strongly about but we did have the conversation.
But for anything else the most important thing is the task getting done.