Upgrade cycle will never end. It is just slowly transitioning into same thing that happens with clothes, which is called fashion. People throw clothes away because new clothes become "fashionable" and because they want to show they can expend effort to follow current trends.
For the same reason a lot of people will not be upgrading. Because they have utilitarian look at old clothes or old computers and if the new computers do not offer anything else than to just differentiate from the old, they just don't see any value in it.