Gaming the rep system is a fault on Amazon's structure. If people in China are doing this without repercussions then what is stopping other people across the world from doing the same?
If export volume is the only factor, we'd expect to see e.g. Polish companies sending seeds at about 10% of the volume coming from Chinese companies.
One possible explanation is that EU exports frequently stay within the EU, so Polish companies would be more likely to try to get fake reviews from e.g. German customers.