Zipp didn't have the market share (in terms of making something radical stick) or engineering expertise (in terms of making it function well) to make 4 arm work at the time (think Mavic Zap - years ahead of Di2, but it took Shimano to secure mainstream acceptance of electronic shifting). For a start, they used very lightweight traditional rings, and an evenly spaced 4 bolt pattern, leaving the heaviest pat of the pedal stroke relatively unsupported. The current crop use more substantial rings and an asymmetric bolt pattern which should be inherently less flexible.
But the main point is that with Shimano dominating the market as they do, and only now offering 4 arm down to 105, the new standard will prevail. Sure FSA and Campagnolo have a tiny market share, but even so, 4 arm does look like the future. I am not arguing for it or against it from a performance perspective (I run Campagnolo and haven't tried it yet), but I am making the point that the industry seems to be moving on. .
I take your point but there was nothing wrong with the Zipp crankset, just the rings. The even spacing must be less relevant than you think, as I mentioned before, mtb cranks have been doing that for years, admittedly with smaller chainrings. Also, Shimano were already using substantial chainrings with the 7900, so they haven't really changed the chainring design with the 9000, just the bolt positioning. On the basis that there as nothing wrong with the 7900 as a mainstream crankset I don't see the reasoning behind the 4 bolt pattern other than a novelty to sell to the masses.
I agree that the 4 bolt will become the new 'standard' purely because of major multi nationals pushing it. Slightly concerning though. Reminds me of a line in the film Armageddon that says something like "it's not a choice, it's a lack of options".