Except what normally happens for professional jobs in the US is that someone lines up a new job, then they quit (and maybe take a few weeks off between jobs). In general, in the US, not being able to start a new job for 6 months would be a non-starter in many situations. And, while some occupations may be very hot, depending upon your age/experience/etc. being able to just quit and count on quickly lining something up when you start looking seems risky.
I am not advocating this system at all, merely pointing out that in Denmark there are protections for employees and a requirement for the employer to pay.
