I have asked a few actor friends what they think, and here are their replies:
Stage presence is a tricky thing--sometimes it's hard to stay focused and "connected," but it's wrong to say that some just do not have it. Sometimes charisma, acting, and using your eyes comes very naturally to people, but when it doesn't, there are techniques and exercises that can teach someone how to interact and tell a story more effectively onstage...otherwise why would we have actor training courses at all?
They have to empathize what the character would feel like in a given situation...
There's a difference between indicating and acting. If you were a real person, describing a scenario or interacting with another human being, you would be mentally/emotionally engaged with both the memory you are describing and the person you are describing it too. Part of how we communicate with others is through our eyes. Even lecturers are told to make eye contact with the audience to engage them. Not that dancers should look at the audience, but having thought/emotion at play, especially when interacting with other dancers (their fellow actors) is so key. Sometimes I talk about hating watching actors act "at" rather than "with" one another, and this is part of it too. You have to engage both with the story and others onstage, as well as with what you are doing physically.
If actors and dancers don't believe the story they are telling, how can they expect their audiences to believe it too? Dancers are storytellers, even when they're not performing in a story ballet. Dance can tell stories of many kinds, but a story falls flat if it's not told in a heartfelt and generous way.
That last paragraph brings to mind Balanchine's famous line: "How much story you want?"
I will go ahead and say that I think the attitude that some people just "have it" and some people don't when it comes to using the eyes or acting may be part of why dancers are so inexpressive today. After all, if a ballet master thinks acting ability is something one either has or doesn't have, why bother to try to teach it or draw it out? But really good acting (not just indicating or mugging, which is what most dancers do) is just as much a technique as ballet, with many exercises to develop and focus one's ability. One wouldn't just bring in someone from the street and say "Dance!" and then, when that person failed to do multiple pirouettes, &c, say, "Well, s/he just doesn't 'have it'." But that is what is routinely done to dancers. They've never acted before, just worked on doing their steps correctly and perhaps learned some variations in which they were told "put your head here; make sure your arm is there; really push down into the pliť" and then they get into a company, and suddenly they are expected to know how to create a character, an atmosphere, show what is happening and what they're thinking/feeling nonverbally, "see" things that aren't there, &c. And then if they don't magically "just do it" after perhaps a few rehearsals that barely scratch the surface of what goes into good acting, they're labeled as "doesn't have it" and so they never learn.
Even a dancer to whom acting does come naturally probably won't have the opportunity to use his/her abilities fully because of the simple, flat way in which ballet characters are frequently staged. Peter Martins didn't like performing Siegfried because he didn't get to dance until Act III. When an artistic director thinks that way, what chance does a dancer have?