The answer to this is simple. There are so many things that need to be paid to ensure that it will be clear to be delivered. There are some items that will get stuck in customs and this is okay if people in customs are willing to help you get the items without spending too much money.
The problem is they sometimes charge too much. It can also be a hassle to get the items from them. Some customs officers cannot be trusted too. It is always best to search for a company that can deliver straight to your doorstep as it will lessen the hassle that comes with getting items.