It is easier to start and grow a business when there are less regulations around employees. Every employee in America is also free to walk away from their job without any notice. These are both facts and have allowed for vast commercial growth and innovation in America (and in countries with similar setups).

Whether you (can) take advantage is completely orthogonal to the original question of why the USA is "an aberration in this regard", and I would rather not devolve into yet another rehash about fairness and opportunity.

The actual quote is "nobody is stopping you" - because that imbalance means it's easier for you to also own the means of production. It's unequivocally true, and enjoyed by 10s of millions of small business owners and entrepreneurs which form the heart of the American middle class. It answers the why posed by the GP.

But yes, different places are different and life isn't fair. No need to cutoff any discussion of various economic systems and environments for the same basic retorts.

Depending on your target industry, "a factory" can be as simple as some old yet reliable drill presses and lathes, and then hiring a machinist or two. How is the flexibility to do this "controversial"?

https://youtu.be/xXze8_SzW28?t=431 <---Granted he's got Youtuber money and other gun-sales related money to help, but the concept is the same....he's bootstrapping a factory after purchasing the relevant capital infrastructure using his own money.