I don´t think all of them show no emotion at all, some of them have a very clear kind of emotion going on, at least in my eyes… maybe for you or for everyone else they all seem lifeless anyway, and well that´s ok, is your perception.

There are other times, or most of the times, when yes, I do want them to have that kind of ambiguous expression, or what I think sometimes is more like an absent feeling, I guess I´m not a fan of drawing super showing/concrete emotions, I think like that you are not really sure what is going on exactly in the moment of the picture and you can have your own conclusions, some things are very subtle but that doesn´t mean they are not there, maybe there are a few contradictory emotions happening at the same time etc. I like that, is a personal taste.