The U.S. Internal Revenue Service defines the role of independent contractors this way: "A general rule is that you, the payer, have the right to control or direct only the result of the work done by an independent contractor, and not the means and methods of accomplishing the result."
Also, freelance workers have to pay all their taxes, unlike part-time workers, whose taxes and social security are partly paid by the employer. And part-timers have to show up at certain times and the employer controls them more.
Many people freelance, but definitely more people would love to have a decent full-time job where they don't have to worry about getting work. But a lot of people are finding out that it's hard to keep such jobs now.