The V70 is 25+ year-old design so it uses fairly primitive methods. A series resistor (switched for selection) is an acceptable way if controlling speed of a brushed DC motor driving a blower load. The worst case dissipation of such a resistor is half the motor full power consumption, but the designers also have to consider the possibility of the motor stalling due to worn-out bearings or debris sucked into the fan (or possibly critters).
You will note the one-time thermal cutoff (fuse) mounted at one end to deal with over temperature.
The large physical size results from the required worst-case power dissipation and the requirement that the part should not run (say) red hot for safety and reliability reasons. The resistances are relatively low and the voltage does not much exceed 12V.
More modern cars may use a large MOSFET and pulse-width modulation to control the blower speed. AC fans such as ceiling fans use different methods to control speed.