I would say it is because we are really in the process of re-learning. Speaking for myself, I am finding out who I am on a whole new level ... and learning how to experiance this adult life of mine sober is a whole process in and of itself. I have had to relearn friensships and even relearn relaing to my husband.
A new relationship could offer a big high right now ... but I know my processes could not handle it. I would go into it not fully aware of who I am or what I am doing. I don't know a lot of relationships could handle that kind of start. The newness of a relationship could be like the high of alcohol ... suddenly everythign seems light and ok again. But what happens when that newness wears off?
There are people who meet and make a relationship, it happens. I just know for myself it would be illadvised.