Dealers call it "the most stringent import and export restrictions on cultural objects in the world" and say "private collectors were already moving valuable works abroad before the law’s passage to avoid the new regulations."
The German culture minister would make a good member of the Deaccession Police: she says "Germany spends billions in tax money to promote culture. It is therefore a matter of course that we should protect and keep our own cultural heritage."
In other words, because we subsidize, in a general way, "culture," we now own these very particular items of culture which may or may not have had any direct connection to the billions in tax money that's been spent. All your culture are belong to us.
Some background here and here.