"Born again" isn't maybe such an unusual phrase, but it's come to have a rather specific meaning in Christian circles, and you can kinda tell from the Ngram search: after 1970 the usage skyrockets along with the popularity of the American evangelical movement. Then an actual right-wing Jesus pest gets installed as President in 2000 and it gets even worse.
After 2010 though there's a curious drop-off. I have vaguely felt like Christians are starting to get a little cagey about boasting of their Christianity. It's maybe safer to hide one's Christianity behind coded language and issues that can be spun as irreligious, e.g. abortion. ~Chara