You can't build and develop subject matter expertise on everything. And besides that, contractors are often used to scale when you have demand that you can't necessarily meet with your current capabilities.
I guess I don't understand how your "solution" to this problem scales to the regulatory world outside of Amazon.
Contractors that are all but employees in name (ie, their routes picked, hours required) are not.
If, on the other hand, they're asked to do something and have the freedom to set the price for the task, to accept or reject the task as they see fit, and perform it at a time, place, and manner of their choosing, and they perform this task for several different clients, then it's perfectly reasonable to consider them a contractor. Which pretty much is what the IRS says, as well, as linked by jcranmer above.
I'm sorry this is simply not true. I work for one of the largest Health and Hospital Corporations in the States (They own 25 hospitals and have 60,000 employees) and sub-contractors Are Always told "how, when, where, and what to do, or what to wear,". Always and Without Execption.
Are you proposing a massive overhaul to the legal framework around contractors or just wanting to target Amazon?