Actually you do see alot of girls doing Cub and Boy Scouts "under the table". Meaning they do all the activities (usually with brothers) but have no official status. I remember one girl actually won the Pinewood derby.
Another big difference is when you look at BS popcorn sales vs GS cookie sales. In the BS program the boys can earn cool prizes like camping and fishing gear and after selling a certain amount, money goes into the boys account so they can apply it towards things like summer camp fees. With GS cookies the troop gets about 55 cents per box and that money goes into a pot all the girls can use. It doesnt matter if a girl sells 50 or 500 boxes its the same outcome. And the prizes the girls get? These little pins or stuffed animals.
And GS troops dont do the variety of other fundraisers like BS does like selling trashbags, mulch, Christmas trees, fireworks, or running pancake breakfasts. With GS its all about the cookies.