My bet: Amazon has an incentive to get the trailers but not the trucks <i>yet</i> because they will get into trucks once they can invest in autonomous trucks.<p>Having their own trailers allows them to explore the roboticization of loading and unloading them now. i.e. Kiva Robotics meets truck trailer loading and unloading.<p>Moving their inventory into trucks but still tracked and managed by their Kiva Robotics systems also lets them reduce land costs and possibly even eliminate nexus in certain states for tax reasons since they could have these mini warehouses drive from a low tax state to a high tax state for deployment.