In Germany, Nazi propaganda is illegal. This leaves Twitter with three options when dealing with a user who posts Nazi propaganda:
1. Leave it up, in violation of German law. 2. Delete the user's tweet, even though it is legal in most countries (and blocking it is a violation of the principle of free speech) 3. Block it only in Germany, and make it clear that it has been blocked.
Personally I think 3 is the least-bad option, though obviously others may disagree.