Because you're not optimizing for the success of the law firms or their clients, but for the structure and integrity of the court system. That integrity depends heavily on the fact that lawyers are trusted repeat players who have a lot of exposure and are personally on the hook for any problem. (Moreover, because a law license is not a right, the due process requirements and burden of proof for disciplining lawyers is far lower than for imposing criminal penalties on non-lawyer individuals. You don't need a trial, you don't get a jury, there is no "beyond a reasonable doubt." Supervising lawyers can be held liable for the misconduct of their subordinates with little showing of knowledge or intent regarding the misconduct.)