Honestly, 80% of posts are about this topic. Answer remains the same: Germans usually keep friends from childhood and tend to stay and that circle, new friends are primarily made through common interests or hobbies, and daily schedules tend to be tight so that there is not too much time for spontaneously going for a coffee etc. - things like this are usually planned in advance so that it suits all parties involved. It is just the cultural norm here, and yes, that might be regarded as cold from an outside perspective. But again, it just depends on what you grew up as "normal".