It's not a question of illegal or not, it's a question of whether smokers are able consent to the risks of smoking, and therefore whether the companies are absolved of damages.

Your argument was that minors cannot meaningfully consent to the risks. But smoking is already illegal for minors.

How can a company be held liable for people who choose to use their product illegally? This doesn't make sense.

(It's different of course if they are directly encouraging children to smoke. In that case, they should have the book thrown at them.)