Branded products are usually expensive and the people who produce copies are trying to offer consumers cheaper alternatives.
People who copy branded products are trying to make a profit by tricking people into buying an inferior quality product which looks like the original.
Fakes of some kinds of products can be of similar quality to the originals and be sold at similar prices.
Branded products usually have a loyal customer base so people who copy the product packaging are trying to appeal to that target group without having to create any new advertising for their products.
It’s very hard to create a new idea for a brand so it’s easier to copy a well-established, successful brand.