The standard reason given is privacy for the victim and jury, less jury poisoning if there needs to be a retrial, people can be a little more or at ease, etc.
It definitely depends on the court, OJ's trial was on TV.
Well, they might allow cameras -- "classified" does not mean "no records" -- but any photos or video would also be classified.
They certainly wouldn't allow the media (or the public) in the courtroom, with or without cameras, or allow the media/public access to anything any cameras they did allow in captured.