Why are most genes inhibited in an average animal cell

Most genes must be turned off because cells play specific functions, thereby only a limited number of genes must be expressed in each cell type in order to produce proteins required in the cell  

Explanation:

Gener regulation is a critical molecular mechanism required for normal cell functioning. In consequence, genes are turned on and off depending on the cell type. For example, in the brain, cells that will be differentiated into neurons will be expressed, while genes involved in the differentiation of undifferentiated myoblasts into muscle cells will be turned off. Thus, genes are switched off in order to produce only those specific proteins which are required for each cell during specific developmental programs and functions carried out by each cell type.

this is math not biology xd