You're mixing it all up. When Bill testified under oath he was a witness, not counsel. Only witnesses give testimony and therefore subject to perjury -- lawyers don't testify.
Bill lost his license because he committed a crime (perjury) and one that is particularly offensive when the perjurer is an officer of the court (admitted to the bar).
The ethical rules of conduct reach beyond courtroom practice into your personal life in that manner, especially when it reflects on your fitness to practice. So perjury is an EXTREMELY serious offence to that end.