Analytics platforms label visits without a referrer or tracking parameter as "direct", creating a catch-all that can hide true marketing-sourced traffic and campaign performance.
How GA4 records traffic from Perplexity Comet and ChatGPT Atlas | MarTech
Perplexity Comet often registers in GA4 as perplexity.ai referral, while ChatGPT Atlas commonly strips referrers, appearing as Direct or (not set) and creating attribution gaps.