In a word, prohibition. We learned long ago that, if a vice was banned, people would find ways to circumvent the law.
We now allow under 25 yr olds to buy alcohol legally, which is a definite risk to brain development and deterioration if abused. As an intoxicant, the social and physical risks are worse than nicotine. But beer, wine and liquor are legal.
There is no scientific study linking e-cigs with any health issues. They can be addictive due to the nicotine, but the tar and other carcinogens in tobacco products are not present.
The Surgeon General warning states a concern with potential harm on developing brains -- under 25 yrs old. Also, addiction to nicotine may lead to easier addiction to other drugs.
The biggest risk from e-cigs so far is a malfunction causing it to explode. That's similar to falling asleep with a lit cigarette.
Killing the bill was the right thing to do. Unless it's a demonstrable health or safety risk to the public -- not just a percentage of one demographic -- banning them for everyone makes no sense.