The question isn't "would you prefer a job or cannabis", it's "what fraction of the population is ineligible for consideration during the period when they're job-seeking". We have an extremely tight job-market right now and you're talking about adding a massive frictional force to employment in that job-market.
What is the average time a high-skilled professional (or even blue-collar) worker is unemployed between-jobs these days? Probably a lot less than 90 days, I'd think. And 2 years might as well be forever in this job market.
CDC numbers put the number of people who used cannabis at least once in 2019 at 18%, and it's probably only gotten higher over time. It's probably more like 25% nowadays - and sure that's "once a year" but the real number is likely also higher than a voluntary survey would find.
In market terms, reducing your supply by 25% or 30% is a lot and would significantly push your prices upwards. And if you don't let prices swing upwards enough, you'll get shortages.
On top of that it's just a generally undesirable job. Lots of time away from home, and extreme responsibility and stress, even in the best-case scenario, and they're making it even more unpleasant (the ever-popular "dead-sea effect") as they run out of people to do it. We're already seeing that showing up in similar jobs like nursing.
And then on top of that you've got the DOT requirements that exclude another big chunk of the population from consideration. So they're competing for an even smaller fraction of the job market, and they just aren't paying salaries to keep up with it all.