Its a stupid rule. Fumble the ball anywhere else on the field out of bounds and its your ball where it went out. A fumble out of the endzone should be placed at the goaline.
But, you just said that if you fumble it anywhere else it's your ball where it went out. Shouldn't a fumble out of the endzone be a touchdown then? After all, it's your ball where it went out, which is in the endzone.