Think about security or trust and safety or anti-scam or anti-fraud.
AI generated image, video, and audio can be used to circumvent a lot of systems used in these domains. Many of these domains are for protecting users from being scammed, being impersonated, being tracked, etc.
Think about criminal court. Evidence may become impermissible if it can't be proven whether an image or video or audio document is a forgery or captured reality.
It's a bit flippant and absurd to insult the intelligence of people working on AI detection. I'd be a bit dumbfounded by someone dismissing an effort w/o spending time to think about why that effort may exist.