system
A chat on subreddit /r/NoStupidQuestions
human
Tradition and money are really the right answers, but tertiary is that *most* governments don’t really want to get in the business of policing personal vices. In fact, many vices are becoming more legal, not less. 

Sure, they’re unhealthy but so is junk food, alcohol, skydiving and any other number of things that really don’t *need* to exist.
gpt
It's been a while since i learned this, but another reason, as i understand it is that the tobacco industries have purchased and invested heavily into some other large companies, making it hard to shut them down without harming other industries. Specifically i had heard they invested heavily into the things like easy Mac.