The candela is defined as
The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency $540\cdot10^{12}$ hertz and that has a radiant intensity in that direction of $1/683$ watt per steradian.
Now, I don't see any reason why luminous intensity should be a base unit. I mean, we can just as simply specify the luminous intensity of any source in terms of its frequency and radiant intensity. It seems (to me) that luminous intensity has just been used to clump the two parameters together.
Contrast this with the definition of a meter
The meter is the length of the path travelled by light in vacuum during a time interval of $1/299 792 458$ of a second.
Now, in the definition of a meter there is one key player, namely light. Even though this definition is given in terms of second (as candela is given in terms of frequency and radiant intensity) but it also refers to a fixed fundamental 'thing' in nature: light. It is primarily on the properties of light that this definition is based, and we require experimentation to determine the 'length' of a meter. This is similar to the definition for a second which refers to an actual real-world object, namely a cesium atom.
But I see no such reference in the definition of a candela. Why is candela a base SI unit then?
EDIT: As pointed out by some in the comments below, apparently candela has been chosen as a base unit considering its usefulness in other fields (quite unrelated to physics). So I guess my question is modified then to: Is there any rationale from the standpoint of physics to choose candela as a base SI unit?
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