Guards can not stay in front of the opponents and that makes lots of pressures on big men (Teague, Ellis,Parker etc). Either Kanter seems more hesitated to show up for the guard or stay with his man or Favors tries to cover two players at the same time.
Quin is obsessed with playing one and one while defending an allstar to prevent perimeter shooting (Dirk, Millsap, Hibbert) No double teamcoming from help of forwards etc
Experience, chemistry, lots of training are elements of defending well and Jazz has less of these elements. Also, playing smart enough against different opponents is matter to defend. Playing set offense against Rockets and increasing the pace against Pacers help efficiency for the defense.