Those were complementary players to a team already loaded with hall of fame players. You're not going to find a Jim Kelly, Thurman Thomas, or Bruce Smith in free agency (unless they're on the last gasp of their career). You're especially not going to get those types of players to come to Buffalo with the current view of the city and franchise.
Once you have elite players to build around, then you can acquire quality complementary players in free agency. As of now, we have no elite players to build around yet.