Why isn't it cool to smoke cigarettes anymore?

Who said it wasn't and why do you care?

it was never cool, just wrongfully perceived as such

inhaling chemicals and poison, isnt cool its not associated with fashion is associated with tramps

10 % of the population is allergic to it. In a sense, smoking in a room is equivalent to putting a sign at the door saying "no gays allowed" or "no lefthanders allowed" or  "no coloured people allowed"

because everyone vapes now and thats whats 'cool' now.

Because they kill you. If I knew the risks 40 years ago I would never have started.

Mind you my grandfather lived until 98 and smoked like a chimney so hopefully I got his genes.

As the others said, smoking is dangerous for your health.

But an other factor which makes it significantly less cool, and now makes people smoking in public be regarded very badly is that it's also dangerous for the people around you.

Taking risks for yourself could be considered cool in some contexts, but imposing risks on others is mostly as*holish.

Because it's a carcinogen, breathing someone else's smoke can cause harm, it's a smelly habit, it's an expensive habit, and the tobacco companies are doing everything that they can to keep addicts and to generate more so they can keep snorting blow off a hooker's boobs.

It's not cool to take an addictive poison into your lungs. Moreover, smoking stinks up your breath, clothing, hair, etc.

It never was, it has always been dangerous for your health.