For Israel, the costs would be more diplomatic: a deterioration of its relationship with Egypt, which is playing a crucial role in brokering the ceasefire, and a further lessening of its regional and international standing following the likely increase in civilian Palestinian casualties. What's more, if mismanaged, a ground invasion could actually weaken the popularity of Prime Minister Benjamin Netanyahu and his government, complicating their path to victory in Israel’s Jan. 22 elections.
Enforcing a ceasefire and avoiding an escalation is also important from a broader regional perspective. Between an ongoing bloody civil war in Syria, mass-scale anti-government demonstrations in Jordan, and brewing unrest in the West Bank, a military escalation between Israel and Hamas risks bringing further instability at the regional level – and distracting regional and international actors from these other crises.
A ceasefire seems specifically in the direct interests of a number of regional stakeholders, led by Qatar and Egypt.