Rainforests are cleared up because of the following reasons:-
Cutting of trees in the rainforests by the logging companies is to obtain timber. They cut large trees like teak; mahogany for making furniture and the smaller one is used to produce the charcoal. The trees with quality wood are used to obtain timber and other is for wood chipping.
Rainforest are cut down for growing fruits, cereals, pulses. The area in tropical countries where all these things are grown was once a rainforest. Vast plantations of palm oil, pineapple, sugarcane, tea and coffee are done on these lands along with the cattle ranching and the soil gets exhausted and cannot retain its qualities for a long time. So the farmers move on for more land and cut more trees in the rainforests.
Rainforest of south and Central America has burnt to make the land for cattle farming so that beef at low cost can be supplied to China, Russia, and North America. For a pound of beef 200 square feet of rainforest has been cut down. The soil without trees becomes dry and exhausted very quickly. The grass begins to die and after a period of time the farmers have to move further and cut more forest because the earlier land has turned to a crusty desert.
Metals like aluminum, copper, gold; diamonds and oil are mostly found below the ground of rainforests. So to obtain these metals we have to clear up the forests. Sometimes chemicals like mercury is used for the gold to separate it from the soil and these chemicals further goes to river and streams and also pollute them. Harm the fish and other aquatic animals.
Oil companies are destroying the rainforests in order to find new oil deposits. Roads are constructed so that pipelines can be placed for the extraction of oil. Sometimes the oil rupture from the pipelines and get into the neighboring areas of forest which damages the wildlife and water supplied to neighboring villages and lands.