The whipped cream I have seen and used was already sweetened. Cool Whip brand whipped cream comes in a container:
Whipped cream, whipped topping, whipped heavy cream - all the same thing.
Cream containing 30% or more butterfat can be mixed with air, and the resulting colloid is roughly double the volume of the original cream as air bubbles are captured into a network of fat droplets. If, however, the whipping is continued, the fat droplets will stick together destroying the colloid and forming butter; the remaining liquid is buttermilk.
Confectioner's (icing) sugar is sometimes added to the colloid in order to stiffen the mixture and to reduce the risk of overwhipping.
Milk resists the whipping and does not hold the air bubbles well. Light whipping cream contains 30% to 36% butterfat and holds air bubbles when whipped. Heavy cream contains 36% or more fat.
So they DO put sugar in it.