China identifies "choke points" most packages pass: large platforms and logistics companies. Yes, Chinese e-commerce is more centralized on Alibaba/JD/PDD etc, but there are actually much more logistics companies in China than in EU.
They also do not introduce these regulations "from tomorrow" (well, sometimes they do, but it's a different topic). E.g. the non-degradable plastic regulation was issued in 2020 to come in effect in 2025. This gives time to prepare and implement (unlike EU border controls mess...)
So now if something is shipped in non-degradable plastic, the logistics company is fined along with the sender. This is much more scalable and easy to implement. Logistics companies might rise their prices a bit in light of expanded work scope, but it would be peanuts compared to every individual seller.
Could EU just ask DHL/Hermes/whatever to charge an additional €1 "for recycling"? Yes, but...
But of course EU is fundamentally different in a way that the politicians need to please the electorate, so nothing is really planned ahead.