Because being pulled over for an illegal lane change is acceptable to the courts.
Knowing to follow someone down the highway until they make an illegal lane change, because you received intelligence from DEA/NSA electronic surveillance not approved by the courts, is not acceptable to the courts.
And that is only a problem because the enforcement capacity does not exist to pull over every person who makes an illegal lane change. The solution is, as always, more surveillance.
Knowing to follow someone down the highway until they make an illegal lane change, because you received intelligence from DEA/NSA electronic surveillance not approved by the courts, is not acceptable to the courts.