Most food chains are limited to 3 to 5 trophic levels for a couple of key reasons.
a) The higher the trophic level, the larger the organisms: As you move up the trophic levels, organisms tend to be larger. Larger organisms require more resources and have fewer natural predators. This makes it less likely for them to be preyed upon, leading to a decrease in their population density. As the availability of larger organisms decreases, it becomes unsustainable for ecosystems to support many high-level predators.
b) The nutritional quality of existing biomass decreases with increasing trophic levels: Energy transfer between trophic levels is inefficient. Typically, only about 10% of the energy from one trophic level is passed on to the next. This means that by the time you reach higher trophic levels, there’s significantly less energy and nutritional quality available. As a result, it limits the number of levels that can be supported in a food chain.
In summary, both the size of organisms at higher levels and the decreasing energy availability create a natural limit to the number of trophic levels that can exist in food chains.