I doubt the goal is even to eradicate Hamas, just degrade it to the point they arent a real threat for some time into the future.
Israel will probably regard that as too costly. Hamas is not just a terrorist organization, it is also the governing party in Gaza. Whatever Israel does it can't leave Gaza a smoking ruin without any governance. Also, they'd have to stay a very long time to eradicate a political/ideological movement - and I don't think Israel wants to be in Gaza with boots on the ground at all if they can avoid it.
My guess is this operation is designed to degrade Hamas, demonstrate their powerlessness so they become even more unpopular in Gaza than they already were, and generally make it difficult for Hamas to launch rockets or do much else of significance for some time to come.