To give a couple examples. If a nurse moves to the US and learns he can't practice without going back to medical school, he may opt instead to work a different job and defer his medical career. If a doctor moves to the US and is in the same position, she may choose to remain a stay-at-home mom and let her husband be the primary breadwinner.
There's also the arbitrage aspect here: globally we may have a healthcare worker shortage, but it may be more severe in one place than another. Reducing the friction involved in moving the workforce could allow workers that are in relative over-supply to move to an area with relative under-supply, improving the overall efficiency of the system.
New York and New Jersey did this. In early 2020 (so two years ago). Despite this, they ran into extreme shortages. So now that we've done that, what next?
> If a doctor moves to the US and is in the same position, she may choose to remain a stay-at-home mom and let her husband be the primary breadwinner.
And is she just going to suddenly start working if the licensure requirement goes away? Some might, but a lot won't because they are already parenting. This is what I mean by these policies require years to have an impact.