Ignoring cars for a second, here’s a partial explanation: gun control almost certainly reduces gun violence, while proscribing alcohol almost certainly increases violence (gun violence included). That’s not to say there is no link between legal alcohol/drugs and violence, but it’s probably overwhelmed by the problems creating by banning those things. Also, that’s not to say other mostly socioeconomic factors don’t utterly overwhelm the gains/loses of limits on guns (comparing New Hampshire to Alabama or Texas, I’d say that’s almost certain). But the directions of those respective correlations are pretty defensible.
Then, there is the raw death rate. Alcohol is “linked” to many deaths, but only directly attributable to a subset (I’m not sure how many). Guns that kill people are pretty easy to link directly to the death.
Now, cars: you’re saying there is no talk of making car access more restrictive even though cars actually kill more people than, well, pretty much anything that isn’t a disease? I think they actually kill more people than guns or alcohol by themselves, at least directly. Well, you got me there, but I can comment a little on the psychology behind it. Cars have avoided becoming a moral issue. Cars cause a lot of deaths, but the deaths they cause are sublimated into “accidents” so they can be socially acceptable. Gun accidents are still homicides. Alcohol overdoses are not “accidents” – they’re just overdoses.