They swung and missed thinking Burks could step in and be the guy, that or decided that the team went through Henry and everyone else was just window dressing. Also, Brown was coming off a year where he missed four games and had less than 1000 yards receiving, they may have decided that he wasn't worth a big commitment.
At the end of the day, all other teams have more flexibility on their roster decisions, and they maintain that flexibility by not maxing out every year with a mid roster. There has to be a reason teams aren't falling over themselves to imitate our strategy, nothing that works in this league goes without being copied.