Most mass shooters come from single parent households or dysfunctional family homes. U.S families vary and many don't live near other family members where they can get help and American communities are not like other cultures or countries where they are involved in raising children.
So if a child's immediate family has issues, there isn't an alternative for that child to to go to to help or for a positive role model. And there are very few public positive role models.
The U.S. has the highest number of single parent households of any country. It also has some of the higher number of mental illnesses and lower numbers of mental health workers.
U.S. works longer hours, have less vacation and holidays, so children are left to their own devices more. Our food supply is laden with chemicals that are not allowed in other countries thanks to lobbying and the FDA. (I'd be interested to see how that impacts mental and physical health).
Our public schools are full of physical, emotional and sexual abuse. The latter being higher than Catholic churches and not very well reported on by any media.
Couple that with media addiction (old,new, and social) and the phenomenon of media "contagion" where you get mass shootings in clusters due to media coverage and you have a recipe for disaster.
Given the failure of the war on drugs, prohibition and the context above, not sure how gun control or confiscation would work when Americans tend to work around those kind of things. Even without guns, we now have drones so its only a matter of time before someone uses those.
However, all that generally gets talked about is either gun control or more guns e.g. arming teachers rather than the underlying causes. Kids used to bring guns to schools without incidents for decades until the 90s when you started to have many latch key kids coming of age from homes where parents were never around.