This right here is why a lot of women think this. I have tons of friends in this age range (26-36) who have done the same thing. You hear all this stuff about how risky that method is, "pre-cum! you could get pregnant from pre-cum! My mom had me from pull-and-pray!" but by year 2 or 3 when you have never had a pregnancy scare? One starts to think perhaps there is a fertility issue because you certainly haven't been all that on top of the birth control.
Also, I don't think they are just going for the waterline. I generally use a black powder liner with a flat brush on my upper lashline and sometimes do a touch on the lower lash-line or waterline. It's pretty subtle if you are just working the waterline or working close to your lashes. This...doesn't look like that at all to me. Their eyeliner is like a barely sharpened CoverGirl black pencil dragged fully around their eyes. Flattering for no one. It ages them both terribly and is generally unflattering.