I live in a very international big German city, so we have plenty of expats. But what I notice is that they are generally shy to approach others, initiating contact or driving the conversation actively. They also tend to stick together in expat groups. So it's a turn off for me if I have to carry the conversation. It's easy to blame the people for shrugging off immigrants but I feel it's their duty to check the local concepts and expectations for communication and relationships.

I also feel that this is generally only true for non-western immigrants. Never had any problems with aussies or americans.

I also agree that making friends is very hard in Germany, but absolutely doable. My life hack: use "Neu in $city" facebook groups, go to boulder gyms and be open minded, smile and take initiative. Talk to people! And then build groups, as mentioned in the top comment (atm).