I couldn't make sense out of the "Common Work Stressors" chapter -- who is the target population which served as a base to establish this list? People lifting h

I couldn't make sense out of the "Common Work Stressors" chapter -- who is the target population which served as a base to establish this list? People lifting heavy things usually have predictable schedules. Also, that, as well as exposure to the weather, becomes more problematic with age, exactly when interacting with people becomes easier... Etc. If this is rather an open-ended list -- why not a word about how companies lay off people based on age? Isn't that a common source of stress to many?