If you have an industrial production process which is going to produce a set number of wire sizes, and you want them to be maximally useful for a wide variety of applications, you want a logarithmic scale.
Responding to commenter e2e8: Using 2mm, 3mm, etc. would be substantially less functional.
Once you have a log scale, it hardly matters whether you measure diameter or area, that’s just a constant factor.
In the ideal case, the log scale would have a slightly easier to compute definition for the dilation at each step than the 39th root of 92 (~1.1229).
Perhaps they could use the 6th root of 2 instead (~1.1224). Then every 6 steps you’d get a factor of two. Size 0 could be defined as 1mm diameter (or size 0 could be 1 millimeter squared cross sectional area, with 3rd root of 2 as the step each time).
In practice if you’re wiring a house, it doesn’t much matter.
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One of the reasons the metric system built on a base ten number system is so frustrating for practical purposes is that powers of ten are entirely arbitrary and indivisible, and tenth roots of ten or numbers expressed in terms of natural logarithms are even worse. We’d be much better off with a general-purpose base twelve number system, plus log scales uniformly designed around the twelfth root of 2. [Western music scale, ISO paper sizes, etc. would fit right in.]