This has been an industry trend all along.
Smaller geometry allows more circuits to be packed more closely together.
Higher level of integration means lower cost. In order to restrict voltage stress on the thinned-out transistor oxide, the supply voltages must naturally be lowered. This gives rise to 3.3V motor control DSPs. Lowering the supply voltage to a component brings down power consumption by the component when the component is clocked at the same frequency. Reduced power consumption directly translates into reduced component size for the on-board power supply and reduced system cost.