Yes there is. Workers compensation insurance and other benefits have significant fixed costs per employee. If someone is treated as an employee, they'll be required to work a minimum number of hours to cover those costs.
In many states regulations prevent customizing employee insurance packages to that extent. There are cookie cutter obligations that employers have to meet regardless of the hours an employee works.
Gig economy jobs get around the inefficiencies imposed by labor regulations.
It's not unusual for some departments (like HR) to operate at a loss, with the costs covered by other parts of the business, or for one product to be a loss leader that guides customers to more profitable products and services.
In any case, the problem of covering those costs doesn't go away by making the employee a contractor, but it pushes the cost off to the worker.
it is a unit cost, not a fixed cost.
Most companies don't let their employees work such flexible hours, but there's no reason why they couldn't.