I think that's a very loose interpretation of Availability in the CIA triad.
This looks a lot like using the MITM hammer to crack every nut.
If this is an actual concern, why not deny personal devices access to the network? Why not restrict the applications that can run on company devices? Or provide a separate connection for personal devices/browsing/streaming?
Why not treat them like people and actually talk to them about the potential impacts. Give people personal responsibility for what they do at work.
It’s not at all a loose interpretation.
Availability: Ensures that information and systems are accessible and operational when needed by authorized users
Yes, but also it’s not an employer’s job to provide entertainment during work hours on a factory floor where there are machines that can kill you if you’re not careful.
There’s a famous fable where everyone is questioning the theft victim about what they should’ve done and the victim says “doesn’t the thief deserve some words about not stealing?”
Similarly, it’s a corporate network designed and controlled for work purposes. Connecting your personal devices or doing personal work on work devices is already not allowed per policy, but people still do it, so I don’t blame network admins for blocking such connections.