Why do we believe in and practice polygamy? Because the Lord introduced it to his servants in a revelation given to Joseph Smith, and the Lord's servants have always practiced it. 'And is that religion popular in heaven?' It is the only popular religion there.
It's like that old expression: "Men plan and god laughs. " You sort of see that in the television world, where you have an idea where things are heading and you have a plan and sort of start off in that general direction, but you wind up taking all these side paths and whatnot - if you're lucky.