The IDF was surprised by the network of tunnels. It was much more sophisticated, and much more diverse, than was thought possible. The tunnel network is all but destroyed now, as far as the direct threat to Israel goes. Hamas will need a few years to rebuild things. The same thing is true for the rocket threat, we bought a few years. The price was high, almost 70 soldiers have given their lives. The operation that was done is the maximum the IDF can do, given the other threats, from the North and the East. We could have expelled the whole population of Gaza, but that would have brought the world's wrath upon us, and it was decided not to do it. Though the option was on the table, at one point. The IDF cannot reconquer Gaza, with the civilians inside, fighting only "Hamas." It would cost too much "fighting time," time the IDF does not have.
Because in the North, there is a problem growing, and in the East, there is a problem growing.
