How is “concentrating on the overall traffic” substantially different than concentrating during regular driving, unless it is less focused or attentive somehow?

How is “concentrating on the overall traffic” substantially different than concentrating during regular driving, unless it is less focused or attentive somehow? Aren’t you taking your attention away to a degree from the nitty gritty of tracking the obstacles in front of you and staying in lane? Citing the “long stretches with no cars” case really worries me that you are in fact paying less attention. It is not only traffic that you need to worry about hitting.