Hamas has learned that Israel will hold them responsible for any attacks from Gaza. If Israel hits Hamas' militants and potentially conditions the future release of the 550 militants to complete the Shalit swap on "assured calm", then they will impose the cease-fire on IJ and all the other factions and sub-factions. It's a bizarre situation vis a vis Gaza; Hamas is the ruling military junta but provides no services to its people who are practically hostages; the PA, who has no political influence on the ground, pays all the bills with money donated by Western powers who are nominally opposed to the terrorism that Hamas represents; Israel, which isn't recognized by Hamas delivers enough food to keep Gaza fat despite having no official recognition with the very government that is receiving the goods; their Egyptians brothers keep the door locked on the Rafah side so that they don't get stuck taking care of 1.5 million people and even the Muslim Brotherhood has said that once they are in power, they'll leave the door closed to shipping least Israel be off the hook; so, it should be perfectly logical in this neighborhood that Hamas should enforce the security arrangements to protect Israeli civilians for rocket and mortar fire.
Ex-FM Lieberman: Firebomb attack in Jerusalem a reminder that norm is Arab terror against Jews (Haar
from the article: Israeli killed as a result of rocket barrage on southern Israel