The Jaguars play prevent defense on third down, preventing themselves the ability to get off of the field.
The Saints took their opening drive to midfield, finally stumbling into a 3rd and 14 situation. The Jaguars, understandably, choose to play soft coverage on this third down in an attempt to limit the Saints to a minimal gain and force a difficult offensive decision on 4th down.
Here's the thing -- the Jaguars had to know the Saints were in a four-down situation. New Orleans was just outside of feasible field goal range.