There is a lot of regulatory stuff, particularly around benefits, that push people towards nominally 40hr salaried contracts even if they don't need all 40 of those.
"Salaried" vs hourly is increasingly a scam anyway, but all that benefits stuff is something that would have to evolve. And it could, if people find the political will.
What regulations prevent an employer to give benefits to employees before 40 hours? And how do some employers give benefits before 40 hours despite them?
The contracts I've seen have an explicit floor, not a de facto one. I.E. The contract says the minimum number of hours you need to work. Some countries also have overtime laws which create a ceiling.
Either way it doesn't change that being paid for your output is the realm of entrepreneurship and submitting bids for project work.
Employment contracts are virtually nonexistent here in the U.S. While the norm is “40 hours”, actual requirements vary by employer, may or may not be communicated in writing, and can change at the employer’s whim. If you make under $107,432 per year (which is around starting salary for fresh graduates at FAANG), you are entitled to overtime pay (minimum 1.5x) for hours worked beyond 40 in a week.
At least for my software job in the US, and other salaried jobs I’ve seen, there are explicitly no hours listed, and it’s supposedly based only on your output. In practice though, if your butt isn’t in the seat 40 hours a week or so, and usually more, the boss will be mad.
"Salaried" vs hourly is increasingly a scam anyway, but all that benefits stuff is something that would have to evolve. And it could, if people find the political will.