Because, in that case, the lawyer’s own actions are the issue.
Titles he recorded before he was disbarred are not invalid because he misrepresented himself. Those who acted in good faith based on his lies are not at fault.
In the case of the person calling himself “Obama”, almost all of his actions have been carried out by civil officers of the United States, and THEIR actions are not invalidated by whatever “Obama” has done or not done.