FWIW, when I first got into serious cycling c.1973 as a high school kid with delusions of racing, 36-spoke wheels were pretty much all I ever saw in person. It was to the point that I didn't even think about it - a road wheel had 36 spokes.

Between college, law school (), getting married, having a kid, starting what passes for a career, and the like, I was largely out of the loop from the early 1980s until about 1992. By then, 32 spoke wheels were pretty much the norm, and lower spoke counts evolved over time after that. Aero wheels of various persuasions (discs, four- or five-blades, etc.) had also arrived, but they were pretty exotic.

I am talking about wheels for every-day road use, not track wheels or wheels for TdF TT bikes. And this is solely what I was seeing on the road and on road bikes in shops - I am not claiming that absolutely nobody out there used other configurations. But I was paying enough attention to think my observations are reasonably valid in terms of what most roadies were riding at those times.