Many cars have both daytime running lights and fog lights in the same enclosure. And depending on settings (auto vs manual, etc), the DRLs might stay on at nigh

Many cars have both daytime running lights and fog lights in the same enclosure. And depending on settings (auto vs manual, etc), the DRLs might stay on at night. And cars vary a lot in configuration. It would take a lot for the police to accurately recognize and ticket people with fog lights on when there's no fog.