Honestly, I think it's mostly fear. There are practical reasons to own a gun and be familiar with its use and maintenance, but there are people who have varying levels of fear of weapons on a spectrum from simple discomfort to full on hoplophobia. The same people seem to be generally uncomfortable with being responsible for their own safety, and prefer to live in areas where government agencies are at hand to deal with any kinds of emergencies they may have.
It's the "don't do this, get an adult" mentality extending into adulthood. Once you're an adult, the next level of authority to shunt personal responsibility onto is the government.
Rightly so, because you could get shot just for coming across some idiot who's having a bad day.
There are no "practical" uses for a gun that come up often enough in people's lives to outnumber the needless death from misuse, or purposeful murder.
Since 2007, there have been less than 500 justifiable homicides per year in the US. And that includes all means of defense. So it's a myth that gun owners are somehow more responsible for their own safety. People just aren't using guns for self defense. You know what they are using them for? Murder.
So the people who defend gun ownership are the ones shunting personal responsibility to protect themselves and their communities.
Along the lines of "fear" I would also add that ubiquitous gun ownership is a large reason for the militarisation and overzealous violence in American police departments. Since anybody could be bristling with guns, the police approach many situations armed for the worst. This makes nobody safer.