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

Police officers often choose to conduct field sobriety tests instead of using a breathalyzer to determine if a driver is under the influence of alcohol because field sobriety tests can provide additional evidence of impairment beyond just the blood alcohol level. These tests can help officers assess a driver's physical coordination, balance, and cognitive abilities, providing a more comprehensive evaluation of their impairment level.