Why do Sundew plants need nitrates?

sundrew grow in oligotrophic soil with little nitrates what they can get from their soil they need to supplment with what they catch in order to be able to grow.

nitrates - are used within the plants to synthesis amino acids, proteins and peptides without these the plant would not be able to grow and become stunted. in a natural environment this would prevent it from being able to compete with other plant species resulting in death and local extinction from the environment.