> Personally I assumed the site would be global

The only reason you would assume a site would be global is if your definition of "global" is "works in the US" & you never bother to check for support of other countries. I live in the anglosphere outside of the US & I encounter more than enough US-only web projects for that not be to a default assumption I hold.

Most sites are not global - it's very odd to assume they would be.

Another reason could be that calling this OpenTrafficMap gives an impression that it is similar to OpenStreetMap, which is global.