There's another dimension you might consider here concerning the ignorance and lower general interest in shotgunning; namely, that shotgunning is the least accessible form of shooting to the uninitiated.
Things to consider:
First,
shotguns aren't casual range plinkers -- which is the kind of shooting that most shooters do or have access to. You can take a rifle or pistol to the range, set up a few sheets of paper on a cardboard panel, and have a jolly good casual time trying to get more accurate. Not so much with a shotgun. You might pattern it a few times, or you might find your zero for deer slugs, but they aren't really casual plinkers.
This leads into the next point, which is that
shotgun shooting is more organized shooting. Whether it's hunting, clay birds, or some sort of tactical competition-based shooting, shotgunning caters to organized shooting sports. Most of us live in cities these days, and most millennials who own guns I would venture to say have never been hunting, or were never taught how. This means their exposure to shotguns growing up will have been limited, and unless they pursue shooting with clubs or at scheduled outings, they won't really have the opportunity to really practice shotgunning.
Lastly, if you want to shoot shotguns casually,
casual shotgunning requires land -- which most folks these days simply don't have
. Want to go shoot some pop cans in a ditch somewhere? Knock yourself out, but you aren't going to be doing it at a rifle range.
I've been shooting my whole life. I grew up in a shooting family, doing handloading with my dad and grandpa, etc. Did junior rifle club as a kid, have shot in some CMP matches, cowboy action, etc. But 95% of my shooting has been rifle and pistol. The essential reasons for this are that my dad wasn't a hunter, and all of my shooting has been on ranges. My dad, my brother, and I used to do some casual clay bird throwing when the range was quiet on a weekday evening, and cowboy action called for a
little shotgunning, but mostly stationary still targets. Most of my shooting nowadays is at a local 15 yard indoor range, where all I can shoot is rimfire and pistol calibers. Without access to land, I have to drive a solid 45 minutes or more to get to a range where I could do any shotgunning or high power rifle shooting. This is just the reality of being a city dweller, I think.
In fact, get this. I have a 12 ga. Stoeger SXS that I've owned for about a year. I've even done some work to it, slicking up the action, even preemptively replaced the notoriously weak firing pins with stronger ones. But wouldn't you know it, I've yet to actually fire the damn thing with 12 ga. shells. I've only fired it with .22LR chamber inserts.
I've tried to get into hunting, but I have found it very difficult to do simply because I can't get anyone to take me/teach me -- and this isn't because I'm just an insufferable jerk, I don't think. Rather, it's because I just don't know many people in my real life circles who are hunters, and the ones who are are well established in a particular routine with a particular party on particular land, etc. It just seems tough to get into. I've even offered to just go along as kid brother with no expectation to shoot -- I literally just want to tag along and learn. Never seems to materialize. I can watch Youtube videos about how to process a carcass, etc, but I remain convinced that learning to hunt is the kind of skill that gets passed on through doing it with someone. Someone who knows the local land; which public grounds to avoid; folks who have a good relationship with a local farmer who allows them to use their land, etc. As it stands, I've been squirrel hunting precisely once with a friend. We walked around getting bit up by mosquitos for a few hours on public land, and saw no squirrels.
Anyway, back to shotguns. I don't think it all has to do with video games. It has to do with dynamics of urban life, and all that it entails. Video games is another downstream result of society's migration to cities. We have a whole lot of testosterone and not a lot to do with it. There is no frontier to tame. We have running water and food no further than the corner grocery store or online delivery order. There aren't any more "dragons to slay," so we create our own imaginary ones. City living -- for all of its conveniences and comforts -- has created a rather sedentary and docile life for most men of my generation, and a lot of men just don't know what to do with themselves. This problem is exacerbated by fatherlessness in our society, etc. It's a topic we could discuss for many hours, and only scratch the surface. I will say that you older dudes shouldn't make the mistake of condemning video gamers, as though your own vices somehow give you any moral high ground.
In conclusion, I think it will remain a trend that as folks continue to grow up and live in cities, shotgunning will continue to decline, while rifle and pistol interest will remain pretty steady.