Junk food dont have a chance to kill a person on first try or high chances to kill them withih a year or so.
Tobacco is incredibly damaging but because it doesn't kill you right away we tolerate it.
There's probably a rather grim metric that defines time to death ratio for addictive substances somewhere in a government report.
When you grow up in a society and see results of gambling, tabacco, alcohol and drug addictions around you that usually deter you from a getting into it. It does not deter everyone, but society actually sees the consequences.
Same with junk food and obesity - when you have people in your family struggle with weight, diabetis and tons of related health issues that's give you more healthy outlook on life.
This is why drugs that kill people fast are so dangerous - because you dont see addicts around you who sttugle to find meaning in life for years because heroine burned their brain. People just start to use and die, fast.
It's not even just about food or drugs. This is how Russia wage a war for 5 years with 400,000 people dead via mercenary army. Society dont see the scale of war because almost no one returns so people keep selling their life for $50,000 thinking its a good way to make money or get rid of debts.