And apparently they do occasionally: http://losangeles.cbslocal.com/2013/11/25/search-underway-af... http://www.wjla.com/articles/2013/01/ups-driver-robbed-polic... http://www.ksdk.com/story/news/2013/10/20/3091049/ http://www.philly.com/philly/blogs/delco/Cops-UPS-driver-kid...

This just makes the robbings easier, as you don't have to deal with a human driver. Much less risk involved, and lower prison sentences when you're not threatening a human and just stealing property.