Israel is repeating the same mistakes the U.S made in Iraq, but worse.
The problem is that Hamas, like the Ba’ath party in Iraq, are both a military organisation and an essential part of civil society, so you can’t just kill them all without replacing them with something else.
In the short term, Israel need to police Gaza (as the U.S military did in Iraq). Longer term it is harder. They either need to allow elements of Hamas forgiveness, or train up new police, administrators etc at their own cost.
It is easy to kill for a well trained army. However what comes after is far harder.