It's all about PR. If EU formulates the new law like they are fighting against pollution and plastic garbage, it sounds nice enough to the electorate who are content with greenwashing and won't investigate much. And 99% of population won't ever a hear a word about real issues by the sellers, to them sellers would quietly and imperceptibly start disappearing. But a direct fee sounds more like a tax hike and the same electorate ordering packages from foreign shops would definitely remember that.