Sadly age seems an obvious factor for Biden. His aides have to protect him from reporters questions.
What some see as protection and old age, others (including myself) see as discipline. I think it’s fair to say that the Trump presidency was defined by Trump’s frequent off-scripted remarks. Even when holding a press-conference to discuss one thing Trump would often diverge into a completely different topic, sometimes changing the position of the executive branch in the process. It wasn’t uncommon for there to be opposing statements from Trump, his chief of staff and the VP all in the same week.
Biden is the antithesis of that - and I believe this is a very deliberate approach. He’s acting like the traditional head of state, which means crafting a position behind closed doors, staying on message in front of cameras and not taking the bait with reporters and deferring questions to the people who’s job it is to answer such things (WH Press Sec, Chief of Staff, etc). He’s learned (partially through decades of his own infamous gaffs) that often there’s little to be gained and a great deal of risk to unscripted responses on camera. One could even say Trump suffered greatly
because he so often said things off-the-cuff which were not received positively - had Trump acted more ‘Presidential’(in the traditional viewpoint) he’d probably have outraged fewer moderates and he’d most likely still be President.
That also explains Biden’s entire campaign. Where some saw an old man “hiding in his basement” (note: that was Trump’s attack line), I saw one of the most disciplined campaigns in recent memory. Whereas Trump had HRC scrambling around to respond to every wackadoodle thing he said and thereby allowed him to drive the narrative, Biden resisted that urge. He was the only candidate who didn’t take the bait (including all of Trumps GOP challengers). As a result Trump’s attacks fell rather flat, Biden was able to frame the campaign around Trump’s Covid response, and Biden got the most total votes from any president ever.