Truth is I did not know, and asking around the other 'experts' in the industry has not really shown me that after all this time the experts fully know.
As far as I can make out, when originally manufactured, they need a seam, and the ying and yang design was visually appealing. And ever since it has stuck.
Apparently the laws of the game do not require a seam, and these days a ball could be made without a seam, but the wiggly line is nice isn't it?
And if you tried to introduce a new ball, I am sure the players would reject it. The wiggly line does help you pick up spin which otherwise would much harder to pick, so the wiggly line will be here forever I think.
