Not really arbitrary. Headcount are typically approved in tranches, budget is a lot more fluid. Headcount is also part of long term forecasting whereas again contractors are just a budget item.
"A $100k engineer costs $150k per year all in" vs. "We need to spend $150k to get X done"
I think it has more to do with getting around benefits, usually.
The expense for businesses isn't just the salary, in fact alot of businesses, if they could just pay the salary, would be able to retain / hire more people, but benefits + high salary is harder to take on.
This is a great argument for universal healthcare and a nationalized pension system, but I digress
But you just pay _more_ for the contractors, at least if you hire locally. In my experience contract rates for comparable work any place you'd want to work are typically marked up (at least) enough to roughly compensate for the difference in benefits and taxes.
Especially now that remote for FTEs has become so common, there wouldn't be much motivation to take long term contracts otherwise. That may change if the job market goes pear-shaped, but doesn't seem like we're there yet.
Tech workers are so highly compensated anyway that benefits aren't a huge percentage of the total cost of employment. The main reasons to prefer contractors in times of economic difficulty are: (a) contracts are fixed length, so it's easy to simply let a contract lapse rather than renewing it if conditions worsen/don't improve and you want to cut headcount without having a layoff, and (b) contractors frequently count differently on a balance sheet (as operating expense vs employee expense).
I don’t know the situation in the US but in Germany a large part of basic benefits (your company might offer more on top) are explicitly a % if your salary, to the point where you can say the minimum legally required benefits (and often the minimum is what you get) mean salary cost regardless of how much you earn is about 23% higher than gross salary. When I worked remotely for a US firm they paid me 25% more on the advertised gross salary to compensate for not being able to offer benefits abroad (I was a freelancer as they didn’t have a German subsidiary), which sounds like not that different than the German overhead.
Average salary for a lawyer isn't that different than for a software engineer (slightly higher). Doctor's average on the other hand is more than double.
if you are one, you are not the other (type of lawyer), in same vein as dentist will never be GP or neurosurgeon or dermatologist and vice versa. you also don't see linux admins leading development of some software projects
any lawyer you try to hire in the bay area will be charging you $700+ per hour. doesn't matter if they work for a big law firm or not. the lowest I ever paid a lawyer was $400 per hour.
"A $100k engineer costs $150k per year all in" vs. "We need to spend $150k to get X done"