Since a series resistor is by definition in series with something, it is one half of a voltage divider. One way to address this is to separate the universe into two types of electrical energies - signals and power. Signals are low power and don't deliver significant energy to wherever they are going. Power is high power, from small audio amps to megawatts, and usually drives a load directly.
OK, those are very coarse definitions, so everyone calm down.
To adjust a signal, which normally comes from a relatively low output impedance source and goes to a relatively high input impedance destination, a two-element voltage divider can adjust the amplitude without being dependent on the actual value of the input impedance to complete the attenuation and set a specific amount of attenuation.
To adjust or limit power, such as limiting the amount of current through an LED or motor, a series impedance works directly with the load to set the power level. Yon can have a shunt element in parallel with the load to further adjust things, but that is less efficient, and expensive at high power levels. Also, the total load power usually is known, so its characteristics can be a reliable part of the attenuator design.
ak