I'm Dutch but not particularly knowledgeable about this, but as far as I understand it the reason being a ZZP'er is so popular is precisely because you don't have to hand in a lot of money to required stuff like retirement and insurance and stuff.
The types of zzzp'ers I'm most familiar with are in construction and they are cheaper than traditional businesses. They're outcompeting traditional businesses because they don't have to pay retirement and insurance and all that.
It's been a topic for years here what to do about ZZP'ers because if something _does_ happen to one at work (ie an accident to their health or to the house they're working on it whatever) they typically don't have insurance which leads to big personal problems for them.
It's like a high risk high reward type of thing, but the issue is that they're also outcompeting traditional workers all over the place.
Otoh, if you were to require them to pay for stuff like insurance and retirement, the whole idea of being a zzp'er will cease to make any sense. You don't earn any higher any more, you will need to charge more so people have no reason to prefer your services over traditional ones.
Zzp'er just means that you work alone and have no personnel. Ie,
similar to a freelancer basically.
Also sadly enough, often zzp'ers are less skilled than traditionally employed individuals. Not exactly sure why that is but might be related to how they were trained and a lack of institutional knowledge due to not working with an established workplace/having regular colleagues etc