Driving isn’t a right. No matter how steeped the US is in car culture, it’s important not to lose sight of this.
Now blood tests show a 12-24 hour window of usage. Much tighter than the 2 to 30 days of other tests. In terms of window of time, that’s essentially good-enough.
Of course anyone who consumes cannabis has a strong desire for a tighter and more accurate test, but you’re really fighting against growing masses of irresponsible users.
If the problem is truly wide-spread like alcohol was (and still is), it’s just a matter of time before states or feds push for a good-enough (for the rest of us) solution.