A possible explanation to the connection between the Ogier and their steddings may be the TP.

In the "Dragon Reborn" when the crew is in Illian, Loial is worried that other Ogier from his Stedding will find him. They find that all Ogier have left the city and Lan latter states that Ogier are sensitive to some things.

It seemed strange that I could find no pre-breaking refference to Steddings, so I have concluded that then the Ogier didn't need one. Why?

I believe that when the Bore was opened, it was not only an entry point for the DO to touch the world, but also the point where his TP could get through. When the bore was sealed by LTT, there was still enough of a hole for the TP to get through. The evidence of this is that the Forsaken have access to the TP although the DO is not loose.

I believe that the "things" Ogier are more sensitive to include the TP. I think that since the TP can be accessed anywhere but Shylol Ghul and Steddings,the Steddings are the sancuiary the Ogier need to stay alive and that over-exposer to the TP outside the Steddings is what causes the Longing.

I also believe that the TP is what is erroding the Seals to the DO's prison.