Why don’t men button the bottom button ?


Why men don’t button  the bottom Button on a suit  ?
A really common habit between men is that they never button  the bottom button of the suit ? why that ?   A  report in the American magazine ‘’ The Huffington Post ‘’ indicates there is a legend behind that , the legend says that Eduard the 7th the king of Britain when his belly become bigger to fit in his suit so he gave up on the second button so others in his palace followed him so he will not feel uncomfortable and it became a habit since then .
Other theories other elegant men who wanted to wear their fancy costumes even when riding a horse , always according to the Huffington post now the jackets f of tuxedos have generally 2or 3 buttons and closing all the buttons will make it non comfortable and not flexible when moving or sitting and could damage the texture accordingly to Kleiv Danilo from the design faculty , one button in enough to keep both the elegant look and flexibility . 
The question is when there is no need to ? weird but it is very common in  between men all over the world .