Mark,
Always reminds me of a demo I saw of robotic mowers years ago. Where the driver would sit was a big box of something. Salesman asks super if he could get used to a motionless unresponsive object on the seat. Super replies, "I get that now!"
You make the same point I was trying to make, its a whole lot of decisions made by individuals in related fields. As noted, design fit maintenance machines through the 70's. HDPE drain pipe reduced the cost of drainage, and was reflected in design. Earthmoving became more efficient thanks to Cat, and was reflected in design, carts required cart paths.....then more cart paths, as a full loop was nearly inevitable. The list goes on. Superintendents came up with a lot of neat, but unpublicized ideas they shared with friends. Golfers wanted smoother, faster greens, and so on. Everyone had their own interests.
And, a few designers made a conscious choice to do something different. More didn't. The new style was a reaction to what had consolidated into a more or less standard pattern. But, like everyone else, those designers changed style believing it was in their best interest to stand out in a crowded field.
Its even harder to pick out one single reason or point in time, it is just a gradual, slow march forward.
And, as I have said before, there are probably seeds of post minimalist design thought out there, if you know where to look, which will only be recognized at some point in the future. No design style solves all problems, no design trend is permanent.