I'm blind and I think that's a good question. Speaking for myself I was taught to look in the general direction of people I'm talking to, but I of course can't resolve with enough precision to look at their face/eyes. I also am blind more or less from birth, so my eyes kind of do their own thing and I have very little to no autonomous control over them. It may be different perhaps for people who had sight before, I don't know.

One other factor: some blind people aren't entirely blind. They may be able to see where you are, even if it's with very little detail. It's easy for them to look at you because they don't have to locate you exclusively via sound.

Other blind people see no detail at all, or see literally nothing (a friend of mine lacks eyeballs completely), so they can only "look" via hearing. They'll have a pretty good idea where you are, but if they lost their sight young, it won't be their instinct to look straight at you as that's a bit of a learned behaviour.

Interestingly, I've learned over the years not to worry about making eye contact with my blind friend, because she can't tell anyway :)

I had vision for 30 years before losing it two years ago, so I still possess all of my sighted conversation traits. I still do my best to look in the direction of whoever I am speaking with in order to remain engaged in the conversation, although sometimes I will turn my head so that I may hear them better, but ultimately I just personally feel that it's impolite not to look at the person I'm talking to just out of habit.

As a teacher of the blind and visually impaired, it suggests to me a lack of social skills if a blind adult is not looking toward the voice or person he is speaking/listening to. Of course, though, it's not always that simple an answer.

I've never looked at people while talking to them, not even when I had sight, because it's pointless and I hate to smell other people's breathes when they are close.