There are probably a few decent reasons to keep the list of participants closed. It does cause several problems, though. The network aspect suffers and it’s hard to tell if the different tracks are suitable for the variety of attendees.
Jacob Hancke made an even more important point: As we entered the room, he shook hands with everyone, asking them what they did and where (I tried to keep it real). He wasn’t provided with attendee-information, so it’d been a bit hard preparing his talk.