So "not enough to live on" often means, it does not even pay job related expenses! Employees are subsidizing their employers!
My partner had a good job offer, but is at home! Buying extra car, petrol, child care... We would loose 150euro a month...
People owned houses and cars by working at grocery stores. A single income from any white collar job supported a stay-at-home spouse. Teenagers bought cars by working part time. College kids paid their tuition and living expenses for the full year by working summers.
That today's below-poverty-line job still leaves someone better off than being completely destitute is beside the point.
You seem to be confused about the point I'm making, which is that low-paying jobs drive people to take on more employment, not less.
So if person A takes 3 jobs just to get by, there are fewer jobs left for person B. (Not quite 2 jobs less, because it's not perfectly zero-sum, but generally at least 1 job less.)
So while I certainly wouldn't make the claim strongly, as I don't have any data, it would at least make sense for the lack of living-wage jobs to increase unemployment rates.