If a large number of people who are already credentialed for a job get it, and then quit soon after, why would it be rational for someone to spend their own tim

If a large number of people who are already credentialed for a job get it, and then quit soon after, why would it be rational for someone to spend their own time and money pursuing unpaid training in the hopes of also being hired onto that job? It seems to me that companies have unrealistic ideas about what they need to do in order to attract employees. Start training again. Cross-train, even, if the boredom issue is a real one. Make work floors more hospitable (provide heaters/fans, lower noise, etc.). There was a time when typists and "computers" worked regimented shifts in sweltering/freezing, warehouse-style offices, too; very few workers will put up with being triple-layered at their keyboards or drowning in their own sweat these days. Maybe that needs to change for trades; or, businesses need to pay more to reflect the trouble people are putting themselves through for their paycheck.