Question

Why does a food chain consists of a few step only ?

Answer 1

Since so little energy is available for the next level of consumers, and for this reason food chains generally consist of only three or four steps. The loss of energy at each step is so great that very little usable energy remains after four trophic levels.
Most food chains are quite short, and they rarely consist of more than four steps. This is because a lot of energy is lost at each step. After about three steps, very little energy is still available for use by living organisms. This also explains why there are few organisms at the top of food chains, compared with those lower down.