What's up with UPS?

What is it with UPS? Why don't they bother to knock at the door when they drop of packages? I saw them pull up and I waited for the knock at the door before answering it, but there was never a knock. Then I heard the truck pull off. I then opened the door to find my package sitting there on my porch. Why don't they knock anymore? Have they just gotten lazy, or is this normal procedure?