I would say it is the type of employee attracted to the type of job. These are factory floor jobs that can be done by those without a high school diploma; some with felony convictions. Low-to no-skill jobs. Exactly the leg-up type of job that can grow to something better. Assembler to job-setter to foreman for one willing to learn.
They assemble parts, and operate machines, sometimes heavy machines, so clean drug tests are a must. I think marijuana testing may be waived these days if you have a medical MJ card - but that will keep you off the forklifts.
Failing the drug test has been a problem for decades. 50 apply, 40 fail, 5 drop out before training ends and 3 won’t last 2 weeks on the floor so 2 are left after a round of 50 applicants. This from a plant that hires from a midwestern city. The plant hiring from rural Indiana has a better track record on drug testing but it is still a problem.