Contractors are usually double what you would pay a salary person in the US too. It is because contractors have less reliable work and pay more taxes than salaried employees.
an employer might pay double for a contractor, but the vast majority of contractors go through middlemen who take a big cut. In my experience, this means that I (the contractor) end up getting about 30% more than I would have gotten as an employee (after equalizing for taxes and benefits.)
I have been able to get independent jobs as a "contractor" where a middleman wasn't involved, but in my experience? those jobs almost always require more work/responsibility for less pay.
Yes, I know, this means I haven't found the right kind of client. I'm just relaying my own experiences. In my own experience, high-paying contract jobs through an agency are really easy to get, but only undesirable clients are willing to go direct with me.
I've spent some time on it... and, for example, have (or have had, at various times) all the required insurance; but there's something else I'm missing.
Contractors (on a 6-12 month contract) actually do get paid better significantly than permanent employee counterparts.
With long term contracts that provide reliable work, contracting pays well. But without benefits.
The UK, and many other EU countries, also have excellent ‘free’ healthcare.
I won't argue that contractors will probably take home more even taking benefits into account, and the tradeoff is then between more stable employment and a bigger paycheque.
That can all admittedly be solved with money, given enough of a pay difference, though in some cases it would have to be a quite large pay difference. The stickiest part used to be the health-insurance part, which was hard to buy outside an employee risk pool if you had preexisting medical issues, but that's mostly been fixed (or at least papered over for now).