The way I look at this year's situation is this one:
If the Heat win, LeBron doesn't opt out and the rest of Big2 + kneejerk Wade do neither. Heat looked vulnerable all year long, suitors were getting in position.
If Dolan doesn't sink the ship, goes from hero to zero, Melo waits until next summer to recruit a competitive team for NY(This is a very unsafe assumption. He's clearly in love with $ so this is an opinion that's very debatable IMO, but there is a chance that he falls in love with winning if this year doesn't go wrong)
The Suns are projected to win single digit games and sniff on the 8 seed. That creates another buyer.
Toronto tries to blow up the team, tank for Wiggins by trading Gay only to create a highly efficient squad. If they tank successfully midseason, Lowry is another guy on the open market. So is Patterson and Vasquez and DeRozan is getting shopped instead of Toronto being a shopper.
As a consequence from LeBron opting out and Cleveland lucking the lottery, we have another free agency player who wanna exceed the cap next year with the Irving extension and utilize tzheir cap space this summer. They become an extra shopper.
Detroit gives SVG full control, he becomes a shopper.
With all the other teams struggling, Charlotte looks like they're a real team. They become a shopper instead of eternal rebuilder.
Atlanta has some pretty good games and guys outperforming their salaries. Suddenly they wanna improve right away as well instead of playing the Houston mediocrity game until some small market team can't afford their 4th all star.
Don't forget Washington taking advantage of the East and lucking all their decisions after Emeka goes down. They become a shopper as well.
This is how these extra shoppers were created. And not extra guys to sign. Most of the guys unexpectedly entering the market were considering only Houston, Chicago, Dallas, Lakers anyways. Just these projected "again rebuilding", "still rebuilding" and "not yet ready to hit the market" teams just were too much for the available crop. That's why less cap space than anticipated will be rent or taken into next summer.
This is what created this Hayward mess in the first place.