Why do complex multicellular organisms do not reproduce by fragmentation process?

Hint: Fragmentation is a process of asexual reproduction that splits organisms into different fragments that develop to form a complete individual.

Complete answer:
The formation of cells and tissue requires a specialized process that cannot be done easily by any simple method. It usually occurs in the case of single-celled unicellular organisms. In the case of multicellular organisms, the process of formation of reproduction is very complex, they require a large number of processes occurring in a sequence to reproduce. This process is also called splitting and is generally found in certain bacteria, fungi, sponges, etc.
Multicellular organisms cannot regenerate easily as in the case of unicellular organisms. The various body parts which are developed in the multicellular organisms are dependent on various complex processes and other body parts. It is an evolutionary process in which the process of reproduction follows various other processes.
In multicellular organisms, reproduction occurs mostly through sexual means where the gametes from both the parent male and female will fuse to form a structure called a zygote. This zygote after many divisions of both nucleus and cytoplasm will result in the development of the various body parts and hence complete multicellular organisms. It is an advanced process that requires a lot of energy and involves many other body parts of an individual.

Note: Fragmentation develops a mature organism from a single fragment, but the developed individual is genetically and morphologically similar to their parents. This process may sometimes occur due to environmental factors. They may occur in animals also but they are primitive and have not developed other reproducing processes.