I think this is a US specific thing.
I work as a contractors with all my clients (who know of each others) and they all pay significantly more per hour compared to an employee. As an employee I could expect to make 1/4 of what I actually make.
The only exception in this arrangement was when I worked with an US company, they wanted to hire me as an employee and paid 1k per month to some company in my country just to hire me. An insane waste of money, not to mention taxes on my side.
US tech salaries are so much higher [at tech companies] that it closes much of the gap on how much more you could earn in a consulting arrangement.
In the US it's not uncommon to have a $200k base. Not even taking into account stock compensation and benefits, you'd need to command about $400/hr contracting to fit your 4x figure. Does that sound comparable to your setup?
Yes: US salary costs include having to pay healthcare fees (it’s not universal here), so work contracted prices are generally discounted by that amount relative to salaries.