It started out as a joke when Harriet Miers was proposed to be a supreme court justice, someone said my dog had been to court more than she had. The really sad statement about that was the Laci probably had been to court more than Harriet Miers!
Likewise, many law school professors have never been admitted to a bar (any bar) let alone have actually practised law.
Other nations provide for some sort of apprenticeship before letting people loose to practise law, but the US legal educational system choose to shift the training of lawyers to law schools. Where did the actual training to become a lawyer take place: in the field or at school? Ultimately, the attitude was that any actual legal education would take place when someone studied for the bar exam in the US. Some law schools try to teach law, but they are not considered the "top" Schools.
Whatever the case, the US legal system sees poor legal reasoning on an epidemic scale. It is worse in the judiciary, but that is due to the political process.