Burying all that straw with tillage would take a lot of fuel consuming horsepower, and increase compaction. The drier the ground the more horsepower and fuel; the wetter the ground the more compaction.

Good productive topsoil down here averages between 15 inches and 24 inches deep, then you reach clay. Sometimes topsoil, at least in some places in a lot of fields, it's 2 inches, or even zero, hard stuff to bury anything in, hard stuff to get a stand in.