Why do some react differently to alcohol than others?

It is complicated. Every person has a different metabolic make up. Some have more active enzyme systems and process alcohol more effeciently than others. It also depends on what other drugs or medications are in you system. Metabolism of alcohol may be slowed or enhanced by these agents. Food also tends to slow the metabolism of alcohol.
Alcohol. Alcoholism is mainly an inherited problem with painful consequences mentally and medically to oneself and to the children who also will bear the gene. Those people have inborn excessive amount of enzymes to digest alcohol as soon as they drink it those not born with the gene, will tolerate only a small amount. Those who binge has excessive enzymes in their system. Binging is thus alcoholism.