I wonder if some of the hackling he has gotten recently in the chance at sports stadiums factored into this decision by his handlers. It is very odd the sitting US president would not publicly speak on the anniversary of 911. To the best of my knowledge for the last 19 years they have always made a speech.
Yeah. He's not allowed to speak out in public. Only in a controlled setting like at the White House or at his home in Delaware.
Had he spoke, I don't think he would have been heckled - not out of respect for Biden, but out of respect for the solemn occasion that was being observed. His handlers, however, did not want to take a chance on him going off script and saying God knows what if anyone did say anything while he was speaking.