Israel closes Kerem Shalom in response to threats by Hamas

Hamas wants to re-open the Karni and Rafah crossings. Opening of Rafah crossing will require a return of European observers and necessitate the EU’s direct contact with Hamas, a major political victory for the latter. Hamas realizes that Israel and Egypt cannot keep the crossings closed indefinitely for humanitarian reasons, and sure Israel will give way and re-open the Rafah crossing.
Hamas threatened to shell the Kerem Shalom crossing at the cost of killing Palestinians. Israel, accordingly, keeps the Keren Shalom closed to protect the Palestinians from Hamas. Why?