Just read this question:
And the first thing that I thought was: why is there so little annual holiday / PTO in the US? 10 days per year for the OP in the thread above. In Germany 30 days/year is typical. (As for unpaid time off, I'd have thought it'd be down to employer discretion.)
Why do workers in the US get so little PTO compared to Europe?
As a frame challenge to your question, I'm not sure that it makes sense to take a (potentially limited) description of one person's PTO availability and extrapolate it to an entire nation's workforce.
I'll use myself as an example. In my current role, I have 26 days of PTO, 12 paid holidays, 5 paid sick days, and 3 days of paid volunteer time (I'm able to take time off work as long as I do volunteer work for a non-profit on those days). At a prior employer, I had 18 paid holidays, 36 days of PTO, and 5 sick days. I have a life to live and value availability of time off, so when I'm selecting jobs, I'm sure to evaluate employers on that basis. Others may feel differently, and may target employers who compensate in other ways, versus time off (advancement, or salary, or other things).
If we assume your theory is true, and there are (on average) less days of PTO in the US, your question of "why" may have many different answers. While there is less regulation in the US than in some countries around paid time off, this isn't inherently a good or a bad thing, as it essentially means that PTO becomes another point of negotiation when working out the details of a job offer. Some people see this as an advantage, since it means they can push for what they want, rather than having their outcomes dictated by regulation. Other people want to be protected from potentially abusive employers and would rather work under a more highly regulated environment. Unions play a role as well, when they're able to act in a manner where they can collectively bargain with an employer to set certain standards for things like PTO.
Further, Workers in the US also have protections in terms of being allowed to take time off for specific circumstances - for instance, if you have to take leave to care for a sick family member, FMLA protects your job under certain circumstances. And we have programs where people out on disability or for other reasons either have protection for their jobs or may receive (limited) pay while they're out. As such, these special cases don't need to be accounted for when an employer determines how much PTO to offer.
I can't speak to the European view on this topic but I consider myself an average American and this is my opinion on this. It's not necessarily the opinion held by others.
30 days paid vacation seems wasteful of human labor resource. I'm not saying 10 days/2 weeks is enough, but 6 weeks of paid time off is unheard of in American culture and seems quite excessive. Employers are paying you a wage to perform some form of labor. There is no reason that an employer should have to pay an employee for labor that they did not perform. Labor is a product that is being purchased by the employer from the employee. Therefore if one is not working, they should not be paid. The fact that paid time off exists at all in many jobs is due to workers demanding it as a condition for taking the job.
Also in America, PTO is used as a bargaining chip in wage negotiation. Often those with high seniority and/or occupying high positions have "earned" more time off due to their position. It is used to incentivize people to to get promotions/stay at a company longer. American's view PTO as a privilege, not a right.
If American companies were to give that much time off, then they would pay less. Personally, I would rather have 20 days worth of pay than 20 days off.
30 days paid vacation seems wasteful of human labor resource" - wasteful to whom? If to you, why are you not working weekends?
There are no laws requiring employers to give any paid time off in the United States. While it is not the only country that doesn't do this, it is not the norm: Wikipedia - List of minimum annual leave by country.
Relevant data from U.S. Bureau of Labor Statistics - Employee Benefits Survey:
Access to Paid Holiday in 2019
Access to Paid Vacation in 2019
Access to Sick Leave in 2019
BLS also has several PDFs on how much leave employees get:
Amount of Paid Vacation at 1 year (Mean/Median)
Amount of Paid Holiday (Mean/Median)
Amount of Sick Leave at 1 year (Mean/Median)
How much a specific employee is likely to actually get in paid time off will vary with the job/industry/location/employment type.
**Private industry workers and state and local government workers combined.
I question the accuracy of these numbers in this answer", then edit the WIkiPEdia page or inform the U.S. Bureau of Labo(u)r Statistics that they are posting inaccurate data.