Why are energy pyramids usually no more than 4 trophic levels?

There are usually no more than four trophic levels, because of the huge loss of energy at each trophic levels. Alomost 10 percent of the energy is lost at each level, as compared to the previous level, which occurs due to wastage of materials like bones and leftover tissues. So, till the fourth trophic level, very less energy is left to be continued to another level, and thus the process is like that.