Hamas' wishes are what's causing this mess.
They wish to attack Israel. They wish to kill Jews. They wish all of these things no matter the consequences to the people around them. It's a bit like Hitler in the closing months of WWII. He knew he couldn't win, yet he kept the war going to punish the German people for failing him. Hama's doen't give a damn about the people in the Gaza strip. Their cause and ideology trumps everything, and everyone, else.