You can make an analogy with the theory of the firm (https://en.wikipedia.org/wiki/Theory_of_the_firm). More workers = more transaction costs. Twice as many people working half as many hours is more expensive; it's more efficient to employ people full time.

You'd expect this to crowd out many part-time jobs, jobs that aren't autonomous and low-context. That is, fast food cook, delivery driver, cleaning jobs etc. can be done part-time, but it's much harder to find shorter hours for white-collar work.