That doesn’t sound like are actual parttime workers, but either freelancers or “small business owners” who get hired.
I dislike billionaires just like the next person, but this also exists in other countries where billionaires either don’t exist or don’t gave the impact.
Part of it is because people think it’s better (at least here in NL) because they earn more after taxes, but in the long term it’s more expensive and because it used to be better for businesses. Now we mainly see a lot of people who wish to work like that.
You can help strengthen an oat if you introduce a third party that punishes people who do not follow the oat. You see that with doctors, accountants and other protected jobs all across the globe.