Disclaimer: Not mine.
There's something about sitting diagonally from Stabler. See, we're colleagues, teammates, but not partners. Same thing goes for Fin and Olivia. They respect each other, will be there if the other really needs someone, but other than that... it's as if sitting diagonally is too far away to become real friends.
It's like a square. The connected sides can be friends, real friends. But you can't invent a line going from one corner to the far corner. It doesn't work. In a pinch, it might. A couple times, Elliot and I, we've been "friends" and the same for Fin and Olivia. But it's never a full time thing.