Why do the researchers use embryonic stem cells instead of adult stem cells?

Researchers use embryonic stem cells instead of adult stem cells because embryonic stem cells are more versatile and can differentiate into more cell types as compared to adult stem cells. 

Adult stem cells are found in mature tissues such as the brain, bone marrow and skin, among others. These stem cells are multipotent and can give rise to a closely related family of cells. For example, adult blood stem cells can differentiate into red blood cells, white blood cells, and platelets. However, they cannot be manipulated to differentiate into any other cell types, which limits the ways they can be used for treating diseases. 

Another disadvantage of using adult stem cells is that they are more likely to contain aberrations, which may be from errors during replication or due to environmental hazards such as toxins.  

Stem cells on the other hand, are pluripotent. They are capable of differentiating into any type of cell in the body and have an almost unlimited developmental potential. They are also immortal and less likely to contain abnormalities.