That's because field sobriety tests aren't designed to find out if people are actually impaired, they are designed to give cops a reason to arrest people purely on their own discretion even when they otherwise lack any evidence of wrongdoing. And in doing so it boosts both the local cops and court's funding through mandatory court fines and fees and programs when they hammer down on people too poor to afford a lawyer.
So whats the solution? 37 people die every day in a crash involving an alcohol impaired driver. Do we think if we inhibit the police's ability to arrest drunk drivers, the world will be a better place? People are clearly not going to stop drinking and driving.
I am neither left nor right, but I feel like I need to say this much more in spaces that heavily lean left -- I wish we would focus on the actual crimes the police are there to stop as much as we do the police reform.
Same with polygraph tests. It's not admissible in court. It's an interrogation tactic designed to give some perceived authority to the police's claims that a suspect is lying and give the suspect a reason to talk more.
Should be illegal.