One more try at explaining catalysts as a concept.
If you are tasked with making the number go down. And you have lets say 15 different causes. (Xenophobia, hate towards people that might have hurt them in the past, frustrations, power phantasies, wish fulfillment, warped sense of no way out, warped sense of justice, uncopable 'failure'..)
You dont necessarily care about the causes. You care about the aspect that might have pushed the number up.
'Easy opportunities to access automatic weapons' - f.e. isn't a cause - but banning it, is a fast and almost guaranteed way of getting victim numbers down.
If videogames could be proven to be conducive to psychotic episodes - banning them, would not be off the table. Currently - there was no conclusive connection found, that they would make you more aggressive if you attended to them for long times, and frequently. They have that effect (aggravating people, inducing 'fight or flight') short term - but after about 20 min it wears off. That said, they can be used to desensitize you towards the act of pulling a trigger when facing crowds, or f.e.peoples reactions in case of a shooting. Those usually werent elements that other forms of media engaged in exploring. Videogames do that readily. If you use shooters to "live out" your violent fantasies this can have a cathartic effect (think Dan Ryckert of Giant Bomb fame stoping to shoot a virtual corps on the ground) - getting it off of your mind - but it can also serve to keep you in those fantasies longer.
So on the individual level - videogames may very well be a part of what made a modern mass shooter. Its just that - many other things may as well.
That stuff is hard to test - in regards to what it does to a "susceptible" mind, because those people are hard to come by for focus groups.
Luckily there are other common factors, that seem to be more worthwile to eliminate than videogames.
Getting attention for their 'manifesto' is a huge part of the motivation. Its not a coincident, that so many of them "took to writing one". Being able to publish and spread it so easily is a big factor in the shooters 'internal reward system'.
Growing up in a culture, where weapons are equated with power - and you have 'national hero' tropes, and prices that were awarded for killing people, and getting Media coverage fore it - is a large part of it. but then it probably also is a large part of how to make a country work, that played 'world police' for 70 years now. (Perpetual wars.)
Having easy access to automatic weapons, is a huge part of someone being able to form even the idea in his (almost exclusively men - also says something (its a self image issue)) head. And a huge part of the planing the execution, and the reason, why there are so many victims in many cases.
Some form of media, that might have been a part of how the 'idea' developed and maybe even became palpable - ranks pretty far down the list.
The point here is, that nobody is looking to eliminate causes (too hard), everyone is just trying to make the numbers go down - if possible. People want easy solutions - that someone else can make/come up with for them.
In the current case, you even had a televised political rally in the vicinity of one of the shootings, where people spontaneously started to chant "do something". (No - you do something..

).
They want easy - single cause solutions - which arent available. And the next best thing is to go after common causes, that might have made the "transition process" from idea to practice more easy. And videogames can be argued to be part of that. Similar to horror movies, or "reading the wrong novel" in the past - but maybe even more acutely so.
Even then they are not the cause. Even then they would not be "what prevents all shootings", but to be honest - people would even take "prevented some of them" at this point. And to bring numbers down - you look at catalysts (what made it easier), not causes. You are looking for single action solutions that have the most impact. And you usually do that by looking at other countries, and there you see - that even though people play videogames there - all other societies have less of a problem with mass shooting than the US - sadly by a large margin.
In the end - we still stay at (the issue has a size of) only double the deaths of people dying from beestings in the US. Which probably is why many politicians, and people can be convinced, that trying to ignore it is actually a viable solution. It probably still could be argued for being the 'best thing to do' all things considered.
But then again - especially school shootings are a real mindfuck, where people give custody to their children away for half a day - with the expectation of safety - so the "you have to do something about this - impulse" is very immediate - and "just ignoring it" seems to be too much to ask, because the entire backdrop situation is so familiar to everyone.
Last time, I kind of ended in one of these threads by stating that at least something is moving this time around, and supporter count for the NRA was, and still is dwindling. So there might be an opening to ban/reduce the number of automatic rifles out there. To at least reduce the number of victims killed per case.
The US at least would not be the first to set such rules in place, far from it.
And to appease the radical libertarian crowd - against something like a dronestrike, those things dont help much anyways. So you dont really 'need them to defend against the state' in the US. You certainly dont need them to defend against neighbors or petty thiefs, either. And if you want to feel big hooting them - then make exceptions for shooting ranges, but keep them there.
Sounds like a common sense idea - but also sounds like a lot of work, and bad blood in trying to establish it. So no one ist too motivated to start it. But then maybe it will happen. Things are moving.