There should be no safety reason to require audio. The only reason for audio is later use for prosecution.
It's not just that they don't want to piss off the lawyers. If they don't provide a private location, then they may be forced to take continuances and recesses so those conversations can happen elsewhere as a condition of not infringing on the constitutional right to effective counsel.
Might be quicker to detect disturbances using audio too rather than video only, think of ShotSpotter. Sounds made up though and probably either a way to spy or chill speech.
It's not just that they don't want to piss off the lawyers. If they don't provide a private location, then they may be forced to take continuances and recesses so those conversations can happen elsewhere as a condition of not infringing on the constitutional right to effective counsel.