Why are highway embankments placed and compacted in relatively thin lifts rather than in one thick dump?

1. Thin lifts allow the specified density and moisture to be achieved throughout the layer; a thick dump often remains loose in the middle
2. OSHA forbids any fill thicker than 6 inches for all soil types
3. Thin lifts are used only so the contractor can bill more load counts
4. One thick dump always produces higher density than several thin lifts