I am not sure if this is getting into the Tin Foil Hat arena, but what if one of the reasons for the Carts is to spy out who is leading a Double Life and to catch the PIMO's?
They are everywhere in common public areas. Like the Stasi of E. Germany.
I know I may be reaching, but we all know the way zealous J Dubs love to rat out anyone who steps out of line.
They can't be there to place literature, because no one is taking it. It's a 3 hour coffee break for most Pioneers.
This is speaking from personal experience.