It's easier to get interceptions in zone coverage, something our corners are not great at. Since our players aren't adept at zone coverage they get eaten alive, especially without a pass rush.
In order to get turn overs in man coverage, the defensive line needs to get pressure on a quarterback, and the quarterback has to want to force the ball as a result. Even if the defensive line is getting pressure, but the QB is up 14 points already, that doesn't necessarily mean he is going to force the ball into tight coverage. This is what we saw against the Patriots, and even then we had some DBs not taking advantage of opportunities. The defensive line played well enough to win that game. This is why I say we need to reinvest in the secondary in next years draft.
Zone coverage needs pressure too to create turnovers, but it has the advantage of having defenders with their eyes facing the qb. The problem with zone coverage is that you can give up a lot of yards in a hurry.
Ideally what we would see here with the return of Randy Gregory is that the pass rush would get to the quarterback a lot quicker and help put opposing offenses in bad situations.