Because looking away may lead to death. When does a deer naturally get suddenly exposed to blinding light? Ignoring the response of "ah it's bright, look away"

Because looking away may lead to death. When does a deer naturally get suddenly exposed to blinding light? Ignoring the response of "ah it's bright, look away" avoids false positives accidentally getting the deer killed. Actual positives never occurred during night time until humans developed artificial illumination.