Why do law enforcement officers conduct field sobriety tests instead of using a breathalyzer to determine if a driver is under the influence of alcohol?

Law enforcement officers conduct field sobriety tests because they provide a more comprehensive assessment of a driver's impairment beyond just alcohol. These tests evaluate physical coordination, balance, and cognitive abilities, which can be affected by various substances, not just alcohol. Breathalyzers only measure blood alcohol concentration and may not detect other impairments.