Why bother eating sweets? Why bother drinking soda or coffee (no nutritional value at all?) Why bother having a hobby? Why bother posting on internet forums?
Because we like it!
ETA: You know, sitting here vaping I realized that if I wasn't using my e-cig I would probably be eating something that wasn't good for me or biting my cuticles or nails. Vaping keeps me from doing something else that I wouldn't want to be doing because I wouldn't like the results of those behaviors. (So I know I definitely have a hand-to-mouth thing.)
My mom is morbidly obese. She has an eating disorder tied to depression. She has struggled with her weight all my life, even on anti-depressants. She had tried everything short of stomach staples to lose weight and always put it back on. I'm not exactly skinny (could lose about 40 lbs) but I know I'd probably have to lose 150lbs (like my mom) if I didn't smoke (now vape.) My family has a history of eating disorders, alcoholism and drug abuse - which I think all stems from a genetic chemical depression that my grandparents, aunts and uncles on my mom's side self-medicating. Ironically, very few of them smoked. I smoked, but didn't end up morbidly obese, alcoholic or a drug abuser. Being "addicted" to e-cigarettes just pales in comparision to what COULD have been for me. The cigarettes could have killed me, but the the vaping won't - and it keeps me from other distructive behavior. I can't see the bad in that.