With a radially spoked wheel, look at a vertical spoke from directly in front or in back. If the flange were made larger the bottom end of the spoke would be visibly higher, further from the axle, closer to the rim vertically but offset laterally from the centerline just as much as before. So the triangle formed by two spokes and the hub, i.e. flange to rim to flange, would have the same base width but be less tall. Thus the angle at the top of the triangle would be larger and the spokes would be shorter. This should make the wheel laterally stiffer. This vertical raising of the bottom end of the spoke is exactly what doesn't happen when the spoke has enough crossings, because the larger flange moves the lower spoke end not vertically but forward or backward.

IIRC and I sure wasn't paying much attention, LF hubs became ubiquitous then as if they were associated with higher-end bikes. But back in the early 70's there seemed to be no consistent correlation between flange height and how "good" a bike was. For example, the Peugeot A08 had LF hubs while the UO8 had HF hubs with marketing hype seeming to claim that HF was better. But plenty of bike, including the PX10 IIRC, also had LF hubs. Howdoyoufigurethat? What's a buyer to think? In the end it is all style except with radial spokes anyway.