Practically every one of my friends either smokes, vapes, or does both.

Of the ones who only vape, most of them will still smoke the occasional dart. They'll smoke them if they can't use their e-cigarette (e.g. out of fluid, left it at home), because they're still addicted to nicotine they'll take what they can get.

There's also the social aspect of smoking cigarettes. I don't know why, but standing in a circle puffing on e-cigarettes just isn't as social as smoking a real cigarette, so if everyone else is smoking cigarettes the vapers will usually have a smoke too.