To limit the probability that cylinders will prematurely deteriorate as a result of coming into contact with the ground, which could lead to the unwanted release of gas, which could lead to a fire or explosion, which could lead to harm to persons.
To limit the probability that cylinders will be mechanically damaged from falling over, which could lead to the unwanted release of gas, which could lead to a fire or explosion, which could lead to harm to persons.
To limit the probability that a fire will spread to and involve the cylinders, which could lead to harm to persons.