It's a combination of subsidies in China [2] and really low Universal Postal Union rates for terminal delivery from China to the US.[1] Terminal delivery in the US is about $1/Kg. Market rate from Shentzen to Long Beach to ship a container is about $1200 right now. [1] http://fortune.com/2015/03/11/united-nations-subsidy-chinese... [2] http://cep.lse.ac.uk/pubs/download/cp396.pdf
I guess they thought it was too much work too.