Why can't we see stars in the sky when earth is filmed from space?

Recently saw the 'Blue Planet' IMAX film which filmed the earth from a spacecraft. No stars were to be seen. Why is that?
Update: I could find replies to dozens of these answers, positive and negative, but I just know there will still be contradictions! My choice of words could have been better ie. shuttle instead of space craft / space instead of sky.......... <quote> If filming from space, it wouldn't be considered the sky.... show more I could find replies to dozens of these answers, positive and negative, but I just know there will still be contradictions! My choice of words could have been better ie. shuttle instead of space craft / space instead of sky..........

<quote> If filming from space, it wouldn't be considered the sky. I'm sure you just meant space ;) It seems everbody that explained light aperature and filmed solved your question. I just wanted to check in on it and star your question, an educated question at that :) </unquote>

Just this one then. Yes, I did mean space not sky. And yes, to all contributors who explained about light aperature, I fully understand the explanations given and concur thank you.
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