The ozone covers the entire surface area of the Earth. Gohan's kamehameha blew Cell into 1 small hole of that surface area. The ozone is just made of gasses that can easily re-form if a small tear like that happens.
This argument is a 1-way battle man. You are asking questions and I am answering all of them. When I ask a question, which has been the same question since the beginning of the thread, your answer is, "I don't have to explain because it was done".