It just so happens that doing that tiny first bit allows even stupid models to navigate the site. After that, advanced models also sometimes query for the data-ai-context and they can mimic the Copy To AI to not have to nav the site.
e.g. content "Job Failure Rate: failed sync jobs as a share of jobs run, per connector per day, over 7 days. Day X: facebook=8 failed / 862 jobs; ga4=0 failed / 196 jobs;"
It's really just an alt text element and bizarrely worked the first time I tried it with old Opus 4.5 and I've kept it. Perhaps the biggest use is giving the agent the short-term token.