Some used a little nicotine, some used more, the Wild West aspect of vaping is why CDC is able to link 250 illnesses with vaping and declare it a crisis when 3X as many people will get sick from raw milk - but no one I have spoken with uses nicotine flavor.
The reason is simple; it tastes like the cigarettes they quit. Instead, they use flavors.
The concern, some real, mostly hype, is that kids who were "nicotine naive" started taking vaping up en masse, and that this addiction is worse for their health than smartphones, caffeine, or video games. Years ago, when our semi-manufactured war on vaping began, I noted that it would probably lead to more kids using them because of the controversy. Kids rebel, kids experiment and, I said, that was a lot better than rebelling and experimenting with cigarettes.
But one thing young people don't do in order to to 'Stick It To The Man' is look juvenile. And there is nothing more juvenile than bubble-gum flavored nicotine vapor. It looks childish, the kind of thing only more self-assured people would do. Adults.