I think the idea is that when vaping, you are able adjust the level of nicotine you are consuming without having to adjust how often you engage in the physical act of vaping/smoking. The act is a comfortable ritual, a chance to take a break, step away, relax for a few moments, whatever. It's a habit itself, distinct from the nicotine dependency. Quitting smoking is doubly painful if you are craving both the chemical and the act. Vaping gives you the act without the chemical.
This doesn't even touch the fact that nicotine is not particularly harmful - simply a habit-forming stimulant like caffeine, adderall or modafinil. Vaping delivers the nicotine without the tar, and the tar is what kills. The thing that makes people nervous about vaping is not the nicotine, but the behavior of the (largely unstudied and unregulated) substances in the vapor being inhaled.
A cigarette has become a somewhat expensive object. When I light it up I would finish it, or at least try to. If the time I had for my smoke break was short I would puff that thing hard to get it done in the time I had allotted. An e-cig can be used for a few puffs and then dropped back into my pocket with nothing wasted. I could be much lazier about how I smoked and as a consequence I tended to smoke less.
That's a big part of the cigarettes many persons (anecdota) have trouble with quitting outside of the addictive properties: the learned habits.