Why are vegetable oils and fats refined ?

The transformation of seeds/beans into vegetable oils and fats involves 2 steps: 

1) the crushing and 

2) the refining

For more details on this, look here

Refining vegetable oils and fats creates an ingredient which can be incorporated into end food product, to meet certain quality and sensory parameters required for those end food products. Refining also makes available to us an indispensable food product in our daily life for salad dressing, oven cooking or frying.

Refining vegetable oils and fats also removes some impurities contained in the seeds/beans, which may accumulate in the crude/virgin/cold pressed oil. Refining retains most nutritional properties of the oils/fats and produces a stable food product. Although crude/virgin/cold pressed oils are available in the markets, using such vegetable oils/fats in end food products may substantially change the taste and texture of the end food product and could be unsuitable for such use. For this reason, virgin oils are mainly used as condiments.