The government could easily fix this by mandating % of workforce be permanent to ensure casuals are only a small part, but they wont do this as it would piss off Coles and Woolies and many other government backers in big business.
That doesn't work. Pre aviation I worked in a highly casualised industry and people were refusing to take full time or permanent part time because it was a pay-cut. Things became a bit nasty as the business expected people to migrate to full time arrangement but the workers refused which ended up increasing the labour cost.
Similar situation in hospitality. Alot of people don't want the full time work and be forced to work. Plenty of staff with side gigs or other responsibilities/interests.
I would be curious in health how many of the casuals would take the full time work with the associated lower pay rate. I'm guessing they can work across a few hospitals and get paid more.