system
A chat on subreddit /r/wallstreetbets
human
This chart must be showing freight, like semi LTL / full load? It would make sense due to the sharp drop at holiday.  

As more companies move online freight should decrease. Hear me out...

Instead of trucking inventory to 10 stores it goes to 1-3 warehouses. Or your warehouse can house higher inventory levels instead of 5-10 inventory deliveries a year you can consolidate to once per qtr. 

Can you compare last mile loads like fedex, ups, etc?

I believe this will provide a more complete picture to support the conclusion.
gpt
This is full truckload volume (i.e. big 53' trucks down the highway).  Upstream that go to warehouses and DCs and some big box stores).  Not the DHL van that delivers to your house, this truckload volume happens before that delivery truck delivers.