I have spent many years focusing on my hands and feet and not on my arms/legs, and the entire clothing industry also has a similar focus. So, I'm not really expecting a lot of appreciation for what I am talking about.
Let me try a couple more points though.
- There is a gradient of temperature from core (warm) to fingertips (cold). The warmer the stuff in the middle, the warmer the blood will be when it finally reaches the finger tips. It is similar to a furnace duct, the furthest ducts will be much cooler due to temperature losses along the way. Some people insulate their furnace ducts for this reason. I am just applying this principle for the human body .. raise the arms/leg temps by 5 degrees and you will get several degrees warmer in the fingers as well.
- The arms and legs are not "complaining" so people don't generally think they need more insulation. Fingers and toes scream pain when they get cold so there is big motivation to protect them.
- Yes you can keep piling on more core layers, but at some point the core starts complaining it is too hot... even when the extremities are far too cold. It seems odd that the core does this, but it is part of our instinctual temperature adaptions which focus blood to the core in cold weather. So, adding more core layers is not the answer. Adding more to hands/feet of course will help, but it gets harder as it gets colder. It might be worth adding more insulation to arms/legs in place of one more increment on the hands/feet.