Why did the British shift the emphasis of exploitation to the export of raw material and the import of finished goods?

It could be argued that Britain's policy of exploiting other lands and people for their labor and wealth didn't change much when they shifted to importing raw materials, then working those materials, and ultimately exporting those materials to the world.

Britain's centuries of colonization led it to explore, and often ruthlessly conquer and exploit, many of the far corners of the world. Britain looked to both the known world, for example India and Africa, and the New World, with its colonizing of North America, to look for new sources of raw materials (and often native populations to exploit, or to import slaves from Africa to work in the New World).

In India, for example, an ancient nation that had an established, exceedingly rich culture for centuries, Indians were often removed from land desirable to the British for the raising of crops like cotton, tea, and spices. British landlords often exploited Indian farmers by paying them little, while "allowing" them to farm lands the Indians may have owned within their families or communities for centuries, skimming off massive profits in the process as crops were shipped to markets in England and elsewhere.

As outright exploitation of foreign lands came to be seen as unjust, many powers like the British switched to the less exploitive system of importing raw materials from lands they had formerly extracted materials from with little compensation to the people of those lands. Often, however, the British still had the habit of leaving the populations of these lands without much to show in he exchange, often supporting native rulers who would ensure that the British gained the most from the transaction.