Why do people write and read fiction or poetry? I believe it's to make sense of the world, to learn about themselves and/or the human condition. Even if a science fiction or fantasy tale has no humans in it, it won't work if there's no humanity in it.
    When you write about the vastness of space, describe dust clouds around planets, or the power of black holes you have to do so in such a way that the reader can relate to them, have feelings e.g. fear of their power, awe at their beauty, or form opinions about them. Your characters might be sentient blobs or have 10 legs and three rows of teeth, but readers still need to care what happens to them, to identify with them in some way. If they're in danger, readers need to be scared for them, or rooting for whatever wants to destroy them.
    Even when a story is set in a distant galaxy peopled by clones and androids, it is the reflection readers see of themselves and their own problems, or at least what they would do in a similar situation that makes it memorable. Sometimes the further the setting or protagonists are from the everyday, the easier it is for readers to gain insights into how they truly feel about issues and principles, and how they would feel. Whether you write kitchen sink drama or space opera, the human element is essential.