"Overproduction" of Snail Mail
Snail mail is definitely not a “level loaded” process during the year, this is a peak time.
You can tell that by the overstuffed USPS box I attempted to use yesterday (to mail something for work, not nearly-belated Christmas cards. I guess it's not practical to size your mailbox for the peak day. Emptying the box twice a day would be an operational option, but the Postal Service doesn't have the financial means to do so right now?