At the end of the day, an employee is just a special class of vendor -- scrape away all of the normative cruft that gets injected into these discussions, and you have a fee-for-service relationship between a customer and a supplier.

And lots of people would rather just be that supplier, who gets paid a specified amount of money for a specified provision of service, and not be forced to bear short-term risk or to hold out for a long-term upside that depends on lots of stuff they have no control over working out for the best.