Hamas had to know that if they massacred enough Jews and rounded up hundreds more as hostages of all ages on Oct 7th,, that this would not end well for Gaza. Especially if you use them as human shields to hide military assets.
Hamas has had almost 16 months to lay down their arms and release all the hostages, and save the good people of Gaza of this grief and chaos, but choses not too, leaving Israel with no choice but to continue.