Speed, safety and cleanliness are the primary reasons.  It is easier for the workers to grab a whole box rather than individual items.  It is also safer for them to remove the boxed wastes from your vehicle if any of the items are leaking.  Also, we do not want any of these items leaking into your car.  We want you to be able to dispose of the items in a manner in which you and the community remain safe.  After all, that is the purpose behind the collection in the first place.