Don't confuse "freight" with cargo, which I use to include everything that's physical stuff.
I don't have a guess as to the magnitude, but, anecdotally, even[1] at peak commute times, I see plenty of dedicated delivery vehicles, as well as people visibly carrying something large and bulky, such as sports equipment[2], changes of clothes, baby stuff[3], and gardening tools.
I wouldn't at all be surprised if the vast majority of peak commute trips are just trying people going "from point A to point B," but even a single, unpredictably time, cargo-carrying trip per week for a particular individual is adequate incentive for having the cability the rest of the time.
[1] or especially, since that's mostly when I'm moving slowly enough to gaze at other vehicles at length.
[2] a friend of mine commuted by train and/or bike for a while and eventually abandoned it, in part, because it meant he could no longer play ice hockey mid-day on workdays.
[3] strollers and diaper bags I've come to recognize, and, if one can extrapolate from child safety seats, there are even more unseen.
I'm not sure what you're trying to get across here, since the cargo also doesn't drive the vehicles, nor otherwise transport itself. It wouldn't exist without the people.
I'd be curious to hear your speculation about how much cargo is actually move by cars during peak traffic volume.