Science fiction that took place in space weren't necessarily predictions. They were imagining what life in space could be like, whether human or not. I don't see how any of us would benefit if every SF author had "realized" that it was unfeasible and just wrote about earth. There was no blind spot, just it did nobody any good to hamper themselves by things like "well, it'll never happen, no point in imagining it". Fiction would be boring if we always only limited ourselves to being completely realistic and true to our current state of knowledge.