One does not simply call other people their friend in Finland.
(This is only my interpretation but I think it's because we have two commonly used words for a "friend" in Finnish. We have "kaveri" which is more like a pal or a buddy, someone you hang out and have fun with. And then we have "ystävä" which we more often translate to "friend" but ystävä is someone you can open up to and have a deeper connection. Calling someone ystävä might take some time. It's not super deep but there is a tiny difference between the two words.)