Because kids love candy. Adults do too, but kids much more.
Kids under 16 aren't old enough to drive, and yet there are plenty of toys shaped like cars and trucks.
Toy guns, movies involving gun violence without R ratings, saturday morning cartoons, television featuring people consuming alcohol, etc.
All of the above can have just as bad as, if not worse, consequences for children should the gateway argument be applied.
This is not to downplay the consequences of minors using tobacco products. It's to demonstrate that just because something appeals to a child does not mean that it should be prohibited for adults to consume / participate in situations that only adults should be allowed to consume it.
Campfires are plenty enthralling - sing along songs, s'mores, hot dogs, etc. There's no calculating the devastation caused by out of control fires, and children definitely should not be playing with it, and yet there's no call to ban adults from enjoying them either.
The whole argument is an ad absurdum, from campfires all the way back to banning pleasant tasting tobacco.
When Alcopops gained prominence in Europe, there was a huge outrage and much talk of bans. In the US, the FTC has investigated the link between wine coolers and underage drinking several times. https://en.wikipedia.org/wiki/Alcopop
Nicotine, like caffeine, has a bitter taste on its own. Ecigs are flavored in part to cover the taste. Lambics aren't fruit juice, ecigs and flavored chew aren't candy. No-one would ever mistake the two.
I'm young enough to remember caffeinated Four Loko being popular in high school. And yes, they were banned/reformulated on exactly the same premise: that they targeted underage consumption[1].
[1]: https://www.chicagotribune.com/news/ct-xpm-2009-08-24-090823...
Most telling is that the article you posted was entirely focused on college age adults, not teenagers. In fact, I didn't find any references at all to underage drinking as the reason why it was reformulated. Am I missing something?