It's important for the exact same reason you're able to ask that question. Without humanity, who asks why? Humanity is, to the best of our knowledge, the best and possibly only chance of increasing understanding of the universe. I care about that, as well as about our species generally in what is likely an evolved and chemically reinforced way. At some point that may be less true, and I would care less (but would still care).
At a meta level, if you truly don't care about the survival of your species (even if only through the survival of your own relatives and loved ones), you're an evolutionary dead end.
At a meta level, if you truly don't care about the survival of your species (even if only through the survival of your own relatives and loved ones), you're an evolutionary dead end.