Why Transformers and AC Generators are rated in kVA instead of kW ?

Why Transformers and AC Generators are rated in kVA instead of kW ?
You all know that motors rating is in kW or HP.
If a motor can be rated in W or kW or MW then why transformers and AC generators should be rated in volt ampere or kilo volt ampere or mega volt ampere ?
Motors
In case of motors, the customer is more interested on the amount of load it can drive to decide which motor is suitable to meet their purpose.
Therefore, Electric motor rating is given in terms of shaft power. The shaft power is the measure of capacity of the motor to drive its load. Therefore, the motors are rated in W or kW or HP.
You know 1 horse power = 746 W
Transformer & AC Generator
The main reason is, the capacity of the transformer is limited by two factors 1. the current that the transformer winding can carry and 2. the voltage it is designed to work without saturation.
In general, the voltage in the power system is kept constant within the specified area. Hence, the transformer voltage and its ratio is fixed.
Therefore, the rating of the transformer is proportional to the current it can deliver to the load. And the load current is always variable and depends on the amount of load and also type of load.
In general, loads in the power system is a mix of resistive and reactive loads. It is a known fact that active power is related to resistive loads while reactive power is relative to reactive loads. Again reactive loads are two types, Inductive and Capacitive.
Therefore, the resistive loads consumes active power and inductive loads consumes reactive power and capacitive loads produce reactive power. The reactive loads do not consume active power. Even through reactive power do not consume active power, they still results in steady current flow between the source and the load. Therefore, both resistive and reactive loads involves current flow between source and the loads.
Therefore, the AC generators and transformers must supply this current irrespective of the type of the load there by loading their wingdings. The load can be pure resistive, pure indúctive or pure capacitive, or combinations of these, there will be always current flow between source and load, Hence, the transformers and AC generators are always rated in volt-amperes or VA and kilo volt amperes or Mega volt amperes.
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