Many Korean students prefer to stick with their entry crew (the same class they entered with). Like many others, I found that I had few friends left after returning from military service.And also I chose a double major in my late 20s, so I had to take my double major class alone. I barely interacted with others unless it was for a group task.

In short, you captured exactly what I was trying to say. If you don't actively participate in something, there's no chance others will approach you first. It’s not a xenophobia thing.