Why dog food packaging is plastic bag?

Only plastic or plastic bags, because the dog food is very heavy, is 10 kg or 15 kg. Now all kinds of product packaging is varied, but all this depends on the value, the design scheme, The packing is beautiful) , convenient transportation, decided to use what the packing quality influence, etc. Packing in addition to plastic bags can also be used for dog food, some plastic blister packing box of these are close to the market need.