It is not so hard to see why and old man, near retirement age and a grandfather, looses it from the younger generation. Usually an abdication results in a younger generation taking over, giving new youth to the monarchy. See Luxembourg, the Netherlands, Belgium and Spain. But when Charles takes over, he will do that on more or less the age on which Jean, Beatrix, Albert and Juan Carlos abdicated their kingship...
In this day and era, so dominated by image and imago, it is not so strange that a fresh young family with cute babies wins it from grandpa and grandma C&C. By the way, in this years open sewers, pardon: comments' sections, I could deduct more favorability towards popular, easygoing, achieving Harry than for the often "lazy"-dubbed William.