This isn’t true.
Purity _______ has been around for forever. When I was in high school, the largest church in our town (FBC) was doing purity shit left and right, and this was the late 90s into 2000. Rings, signed forms, wristbands, etc. The weirdest part was the youth pastor who was promoting this was always seen around high school at lunch, showing up to athletic events (which isn’t too weird but was weird), and generally still trying to be a high school student.
Purity balls (like actual events) still happen in West Texas as my friend went with his daughter back in 2012. I just quickly changed the subject because he believes in that shit but also drunkly told me he was gay.
So no, it’s not something “most Christian’s have never heard of” and in fact, it’s the complete opposite—they’ve heard about and know about these purity balls and tests but because of the blowback of how indoctrinatory it combined with this general creepiness, they keep quiet about it.