The ’70 ball was designed to be visible on TV and somehow ended up becoming the archetypical soccer ball. That is, I think, a pretty cool story. The soccer ball I grew up with, the one I drew whenever I wanted to draw a soccer ball (always looked ridiculous because drawing icosahedrons is hard if you don’t know what you are doing) as a child is actually just forty years old!
But I don’t think that difference is actually that big. Sure, there is the color and it’s a icosahedron, but just look at a volleyball. They still look like the ’66 ball looked. So this change of shape didn’t have to happen. (Recent design also abandoned the icosahedron – it’s quickly becoming a thing of the past.)
The first soccer ball that wasn’t boring and actually recognizable as a soccer ball? Many more people than before were able to see the Worldcup in the 1970s (because many more had TVs)? It was the first sponsored ball and Adidas put a lot of money in Marketing?
I don’t know but those seem like plausible explanations.
But I don’t think that difference is actually that big. Sure, there is the color and it’s a icosahedron, but just look at a volleyball. They still look like the ’66 ball looked. So this change of shape didn’t have to happen. (Recent design also abandoned the icosahedron – it’s quickly becoming a thing of the past.)