The head of the FBI wasn’t invited to the ‘extremism’ summit either... Seems good guys are treated badly and people like Sharpton are invited to the White House weekly... Very strange.
618 days until Obama leaves office...
The official line for not inviting him (and other, what would be, cognizant officials) was to eschew giving an air ‘enforcement’ to the summit. Ostensibly, all there were to work out themes and policies.
The real reason they weren’t there is because they have a sworn duty to uphold the law. And, in the high capacities in which they serve, are obligated to act in a lawful manner. My guess is that Obama did not want them to be confronted with what some might call conspiracy and collusion to violate existing laws.