1. We are culturally different. Their language and dialect, practices are so different, there is no commonality.
2. They are literally separated from us by a huge land mass called India.
3. It's the past. Move on. Stop trying to create enemies where you don't even have enemies.
4. We don't want them back. Most Pakistanis don't. They are doing good on there own, and keeping in mind the distance and cultural distinction, we don't want them.
Now before you call them traitors... i mean what choice did they have. We did wrong them.
If you ever get the chance, see what Musharraf had said about it.