From my experience in undergrad, the Copts just don't know how to reach out to other ethnic Orthodox. It's all about knowledge and excitement for OOxy. Instead, many of those who took my place are great club organizers, but have no knowledge of other churches like I do, and thus are just forced in a position to mostly keep it Coptic.
I have personally tried to avoid this by not making any spiritual adviser Coptic, but rather Indian. But that seemed to have not helped.
In addition, there's also some slight differences in teaching, and many Copts tend to say things like, "Well, the Indian Orthodox priest says this, but I learned this in the Coptic Church" or "Do you see how those Syrians don't fast like we do?" and it becomes part of the discouragement of the Coptic leaders to invite them again.
I'd say the problem is from Coptic Sunday schools. From our youth, we are taught more Coptic pride than Orthodox pride. I did not know we had "sister churches" until I actually went to undergrad.