The small size of the cell is due to the need for a large number of them. For example, the skin would be less elastic if it consisted of fewer but larger cells. Also, a large number of cells allows for improved regeneration.
A huge number of cells are needed in order to distribute the various functions of the body between them. One large cell is not capable of performing all functions, because is an elementary structural unit of an organism.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.