The NFL is a constantly evolving game. Offensive and defensive coordinators spend the entire year trying to identify trends — and ways to exploit them. Nowhere is this more prevalent than in the increasingly more-dominant passing game.
Offenses have figured out ways to carve up static zone defenses through their seams, and ways to beat man coverage through pick plays and exploiting inferior defenders. So as the passing game has become more refined, defenses have turned to zone/man hybrid coverages, which are called pattern-matching coverages.
By taking the beneficial components of man coverage and limiting its exposure to better athletes or rub routes by incorporating some zone techniques, defenses have been able to protect themselves on multiple fronts.