Suppose the benefits cost the company the equivalent of $3/hour. Then at the same cost they can either offer a job that pays $15/hour without benefits or a job that pays $12/hour with benefits. They're not idiots; they're going to offer the one that best allows them hire and retain workers.
That it happens to be the one with the higher pay should be telling us something -- that some workers value the money over the benefits.
Which makes a lot of sense. Many people have a family health plan from their spouse's job. They may value the flexibility of choosing when to take unpaid time off instead of working for $12/hour with paid time off, which is a monetary loss equivalent to more than 10 weeks of unpaid time off when working at $15/hour instead. They simply get less from the benefits than they get from being paid the money it costs the employer to provide them.
Stop requiring employers to provide "benefits" that many employees don't want and people wouldn't have to voluntarily work around it like this, at the cost of being unable to work 40 hours a week even if you want to.
But that's not the case today in the US. My point is that the government mandating that full-time jobs provide benefits (which is the case today in the US) doesn't fix the adverse selection problem. All it does is lead to a bunch of jobs right under the cutoff for full-time.
If as an employer you just can't get a break on the rates it costs to insure you, that's a really strong signal you have something wrong. Doing it through the government in theory gives people freedom of moving from employer to employer, but I guarantee you there is some juju that needs characterization in wresting some of the incentive shaping powers of insurers and vesting them in Government.
It's probably easier to name and promote the few places that don't do the "39.5hr week".
Government, by tieing things that should be universal to mandates to employers who employ a person for a certain number of hours in a week. Which, in addition to promoting this kind of behavior as a cost/utility optimization, encourages a feudal lord-servant relationship between employers and employees rather than a capitalist market-exchange relationship, and necessarily (even ignoring the effect of the optimization incentives) assures that what should be universal is instead limited to a narrower fully-employed class.
If the government provides the benefit universally and taxes to cover the costs, the perverse incentives to limit employment and further narrow access to the intended general benefit is eliminated.
Naming and shaming the people who follow the incentives government creates is pointless; name and shame the government for setting up the broken system of incentives. Any other target is just a perpetual game of whack-a-mole.
There needs to be naming and shaming of those that perpetuate this practice. I know retailers (Tractor Supply) for cashiers.
If you're doing warehouse work, you are part of the logistics backbone, you deserve not to have your chain jerked around. Arguably, no one should be getting their chain jerked around, but I'll call it a win to purge this pathological HR hacking from another business layer.