They were not allowed to trade goods with other countries or go get stuff from them. Otherwise they would be arrested or get cruel punishment. This was a very bad situation for them because they had to make do with what they had and it was expensive since you could not go and get anything anywhere else.
Have you ever been happy and sad? That is kind of how they were. They produced new raw materials... but they did not have much freedom of what they ate and where they got it.
People suggested they use raw materials for markets. There was not many natural resources. People thought that no great nation could exist and be steady if there was no colonial resources because they did not know better.