There are nuances to the whole thing.
Let's start with something important. The definition of 'mass shooting' has changed over the last 15-years and this has been a deliberate shift, IMO, to justify a political narrative. At present, all shootings where 3 or more people are shot are classified as 'mass shootings'. That means any time gang members shoot up another gang and three people get shot? Mass shooting.
By contrast, prior to the definitional change mass shootings were where 5 or more victims were shot by the same perpetrator(s).
Did you catch the shift? Now it is a shooting where three or more people are shot. Not all shot by the same person(s), just shot.
Two guys rob you at gun point, you draw your piece and shoot them and they shoot you - you're now part of a mass shooting.
By contrast the 'mass shooting' definition has
not changed in other countries. So, we aren't comparing Apples to Apples.
This alone accounts for much of the 'substantial increase' in mass shootings in the United States. In other words...there doesn't appear to be one. We do have on average, a higher rate of shootings within schools/hospitals/etc. compared to other developed nations. But this is likely due to accessibility to firearms and poor mental health infrastructure. We have seen time and time again that the individuals who perpetrated these attacks had multiple encounters for authorities who should be able to do something about it and failed. Is that a gun problem then? I would argue no.
That said, The United States has guns in plethora and that provides easy access to those tools to commit these crimes. We also have a sensationalizing media and culture that draws attention to these crimes as well. Both contribute to the ability and willingness to use those guns to commit heinous crimes.
It's important to note that while for instance, Japan, has less shootings, they have had substantial gas attacks and arsonists kill mass numbers of people. And similarly, Japan has found that these individuals where known to authorities in advance of attacks. Are the matches and gasoline to blame or is it a more complex failure of society?
To get a truer sense of this I think we have to remove 'shooting' and look at mass casualty attacks globally, defined as 5+ victims attacked by the same perpetrator(s). Until then, I just start the conversation when someone says, "mass shootings are on the rise in the US!" - by asking them if they know the definition of mass shootings in the US? The answer is overwhelmingly, "No." - And when you point out the definition was changed their immediate response is, "Well no wonder they're on the rise...they lowered the standard."
Yea...just like lowering grading standards results in more high school graduations...