One story to explain it: Space filled a psychological niche for people, which something else now fills. A logical thing for that to be would be the internet and computers. For some of us who are hard core futurists, we also have far-future aspirations like life extension and uploading to concern ourselves with. It's not that we've given up on space, but it is less captivating because it competes with other interesting things now.

This.

Once upon a time the future meant space ships. "Go farther, faster." The future was the flying car, flying farther. The Jetsons. That was before DNA, before nanotech, before life extension, before uploading, before the internet. Before the more interesting stuff we can do right here.