Since CPAs are not required to belong to the AICPA in order to conduct public company audits, the most severe sanction would only serve to save the CPA some dues without any other practical effect.
CPAs can perform audits on public companies without belonging to the AICPA. 
mnli hypothesis: CPAs can perform audits on public companies without belonging to the AICPA.  premise: Since CPAs are not required to belong to the AICPA in order to conduct public company audits, the most severe sanction would only serve to save the CPA some dues without any other practical effect.