The best explanation for why there are fewer secondary consumers than producers is:
Around 10% of the energy is transferred to support the next trophic level.
This statement reflects the concept of energy transfer between trophic levels, commonly referred to as the 10% rule, which indicates that only a small fraction (around 10%) of the energy from one level is available to the next level. This results in fewer organisms at higher trophic levels, such as secondary consumers.