Whether you agree with the rules or not, no-one is exempt from them. Protocol is that no-one takes photos at the hearing, likely a blanket policy for all legal hearings that streaming is controlled as most UK hearings aren't public. The law goes back a long time and required artists to sit in court hearings and create drawings of high profile cases.
Necessary to prevent people tampering with it. Record it, edit it, share an edit, rewrite history. The intention is to have one official, accurate record of proceedings and to stop anyone butchering that. eg. Take a photo, digital manipulate to change the content on a document, share the image.
And yes, it won't stop people, but that doesn't then mean people in the court should ignore the rule or the rule should be repealed. You won't stop people speeding - does that mean we should remove all speed limit regulations? You won't stop people burglaring by just saying they aren't allowed - should we thus ditch those laws?