That's a good point - and there is supreme court precedent to back this up. The supreme court has ruled that the job of the police is NOT to stop crime, nor to prevent it, and they are not legally obligated to intervene even if they see a crime in progress! They have the right to sit on their ass and do nothing. Fact.
Very true - but the original story is about senators wanting apple to pull checkpoint notification apps.
Those same senators could enact legislation to hit bars and limit the ability for drunk drivers to even do so.
Those senators don't - bars make a lot of money and it is cheaper and easier to pin the tail on the drunk drivers. (And not texting drivers, sleepy drivers, etc).