I would add that travel nurses are treated better in a lot of ways. Staff nurses must attend certain meetings and training aimed at standardizing care and improving outcomes. The travelers don't have to attend. Travelers can take off pretty much any time they want as long as they know before they sign the contract. Sure, they're considered "outsiders" by some staff and sometimes get the less enticing patient assignments, but for those drawbacks, they get paid 4x (I've seen 3-8x staff rates, but 4x seems common) plus a housing stipend as long as their location is more than some distance (I think 40 miles iirc) from their "home" location. Why would anyone be a staff nurse?

Anecdotally, I know a travel nurse who works in pediatric ICUs (PICUs). One shift a couple months ago, the overnight staff on her unit was >80% travelers. And this is in peds units that aren't as affected by COVID, because ~1/2 of the patients are cardiac babies with congenital heart issues. The only case I can see for not paying staff more to increase retention is that they can respond to a dip in cases over the summer, but that can't possibly be an 80% decrease in patients. Maybe they're waiting until travel rates come down to offer an increase in pay so their 1.2x salary offer is more enticing in comparison to the travel rates, but the current system is ridiculous financially. I did mention that we've seen first-hand that hospitals can afford to pay nurses $4k/week, though, and I'm sure I'm not the only one who noticed.