 live in-person audience to feed off of. Even reporters will be housed in a building across the street. Trump will be alone in the studio with the only people to feed off of are the CNN moderators, who of course will be cold and hostile towards him. This creates a very sterile academic environment for the first presidential debate, which favors a lawyer legislature like Biden, who is more experienced at this kind of dispassionate debating. Clearly CNN designed it in this way to give the edge to the Democrat candidate.