why did Max have to leave 33 Himmel street

During one of the bombings Max runs up from the basement to peer outside the window. He notices the stars burned in his eyes. I really think that Max needed out of that basement. Max is a fighter by nature and hiding really was not what he wants. By hiding, he is endangering the lives of hans, Liesel and the others. Hans is tired of hiding, he wants to do something. He wants to go back to the real world, no matter how twisted it is, and make a difference. It has been arranged that Max and Hans would meet in the forest in four days; Hans only finds a note reading "You've done enough."

max needs to run because the bombers found him

It was after the incident of Hans helping one of the jews in the march, which could have led people to believe that he was hiding a jew. Max left so that if soldiers were to investigate; they would find nothing, and the Hubermann's would be safe.