Question

Why does a food chain generally consists only three or four steps?

Answer 1

Because after that the energy available for the next organism will be so small that it will be insufficient to sustain the life of that organism.

Answer 2

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.