I think concepts like Spinoza's or Deism or people who declare themselves "not religious but spiritual" are just having trouble parting with the comfort of religion even though they know there's nothing there.
One reason people opt for it, which I find understandable, is owing to the popular connotations that atheism carries, not unlike theism. You can avoid having to explain "I'm not saying I know that God doesn't exist". But the qualifier is explicit. One needn't necessarily be certain whether they believe in a God or not and I don't think that's well represented by the term "atheist". By the same token I don't think Deism is anywhere near atheism-lite. It is explicit belief in a God with the caveat that it's irreligious.
I like the term "apatheism" because it also captures the way I feel about the question of whether God exists.