Not only tunnels. Almost every house was rigged with explosives, like what happened in Gaza city, entire neighborhoods would explode once the troops arrive. If not rigged then it would be a stash of weapons somewhere in the house or under, you are not going to spend days on each house that is potentially rigged looking for a needle in a haystack.
Unfortunately the worst for Gaza will come after the Israeli elections. Israel has 2 years of politically favorable US president to clear out Gaza City once and for all to correct the mistake of 2005 withdrawal.
