There was a period of time where 650c wheels were fashionable for triathlon bikes. The thought was that they were more aerodynamic (shorter spokes, and shorter profile into the wind).

However, once everyone figured out that smaller wheels had to turn faster for a given speed, and that wind resistence is a squared function of speed, they realized that those shorter spokes were moving faster into the wind, negating the advantage, and making them possibly even slower.

So when the aero advantage was pretty much debunked they fell out of fashion for tri bikes.

Note in the Catalog picture in the link, the bike is set up with aero bars.

The other reasons mentioned, such as toe overlap are pretty much limited to smaller frames, whcih is why today you typically only see 650c on smaller frames, often women specific designs.

Again, in the catalog referenced they were using 650c wheels across all the frame sizes.