What?!? Would you employee people full-time and let them work whenever they felt like it?
Millions of people in the UK are legally salaried workers on "zero-hours" contracts, where they aren't even guaranteed a minimum number of hours. Paid through PAYE (payroll), have workers rights, just not a guaranteed number of hours.
Most can choose when they work, many have more than one of these jobs.
It's not a good way to live but it's at least possibly a better way to live than the gig economy.
You can't have an employee on the payroll costing $1,500 a month in benefits who can choose to work 0 hours in a month.
And then the other part of it: the penalty for not having healthcare insurance was deducted to $0 at the end of 2018. So there is currently no penalty at all (other than the massive ones if you get sick) to not carrying insurance.