Scroll down past the accepted answer and you see what is likely the real one. A manufacturer came to the standardization board with a new design, asked for it, probably lobbied them for it greatly, and they eventually accepted it. Reasons for why the manufacturer wanted this aren't stated, I'm sure its a mix of engineering ideas, wishes, dreams and some mix of gaining an upper-hand in whatever market was there at the time.

Obligatory XKCD: https://xkcd.com/927/