Well, other people using the room aren't the only consideration. He eventually gets interrupted (after ~2 minutes) by someone saying that "the final keynote is

Well, other people using the room aren't the only consideration. He eventually gets interrupted (after ~2 minutes) by someone saying that "the final keynote is about to start", so at minimum the speaker will have to hurry to the final keynote; if that person hadn't happened to come in with the reminder, the speaker might have been held longer and been late to the keynote. Of course, she could have excused herself, but it would be awkward and risk rudeness to do that while someone is in the middle of asking you questions (especially once he made an issue of being allowed to ask them).