Similarly the DOJ looked at the Trump hush money case and declined to prosecute.
Campaign finance laws in the US are a land mine and need reform. There is too much prosecutorial discretion and not enough clarity for people to know whether they are breaking the law. Campaign finance laws have become a way to fish for a crime against political enemies.
To wit: Bragg actively campaigned for his position promising to investigate Trump.
Rule of law should be about observing and then prosecuting crimes, not about spending years and millions investigating people looking for a crime that they committed.