It would be unconstitutional for a U.S. state to treat newly-established residents differently than long-established ones with regard to a welfare benefit:
http://www.washingtonpost.com/wp-srv/national/longterm/supco....
Countries like Germany don't have this problem because they have the power to control their borders. Accessing Germany's healthcare system requires being a German resident. That, in general, requires applying for immigration, which the government may or may not grant. EU citizens can, of course, become German residents without applying for immigration, but every EU state has universal healthcare so there is no incentive to free-ride.
And there's a push within Germany and other countries to limit access to welfare benefits for new residents, even ones from other EU countries: https://www.theguardian.com/world/2016/oct/12/german-governm.... U.S. states don't have the power to do that.