I don’t think mirrors are considered in safety tests at all. My understanding is that the only requirement is that you meet the tech specs defined in Section 571.111 - Standard No. 111; Rearview mirrors.. These are all physical properties like the size, mounting and reflectivity. The regulations don’t require cars to have additional convex mirrors, so I think it’s unsurprising that car manufacturers mostly don’t bother to provide them.
I don’t think mirrors are considered in safety tests at all. My understanding is that the only requirement is that you meet the tech specs defined in Section 571.111 - Standard No. 111; Rearview mirrors.. These are all physical properties like the size, mounting and reflectivity. The regulations don’t require cars to have additional convex mirrors, so I think it’s unsurprising that car manufacturers mostly don’t bother to provide them.