"Nones" are not all non-believers. I believe both of my daughters are "none" but I don't think either of them identifies as atheist or agnostic. A lot of people are claiming to be in that nebulous "spiritual but not religious" category. I don't understand that very well.
Additionally, though, exactly how many "Christians" are there? LGBTQ+ friendly Christians will tell you that people who damn them as sinners are not "really Christians." Evangelicals have a much narrower definition of what a Christian is. So, if you're not one of them, should you even call yourself a Christian. I think once they sort themselves out, "nones" become the biggest group.
I look forward to the day when "none" is the default position and theists are labeled as such, although it certainly won't be in my lifetime. As for "spiritual". I haven't a clue what that means.