No Audience is Allowed On Stage During Rehearsals
Before the taping of an episode, rehearsals take place. Ellen rehearses her opening monologue, the production team runs through any games, and the musical guest rehearses their song. When all of this is going on, the audience is not allowed in the soundstage. If these rehearsals take a long time, then it means the audience is sitting outside longer, in the rain or shine.