Because I don't deify nature.

If they believe nature is the highest form of being (or whatever), where does the deifying come in? Nature is just nature. "Deifying" seems to imply that you're raising it up to a higher level than it actually is, and that's not something I do.

Really, it just depends on your definition of god. If you say "god is nature", than sure, "god" exists. But you've just cut your concept of god down a whoooole lot. (In fact, it wouldn't really make sense in a society where many people a members of one of the ethical monotheistic religions.) God as nature doesn't imply any morality, doesn't demand any worship, there's nothing supernatural there. It's pretty much exactly how as someone who isn't pantheist sees nature.