Increase in firepower? or increase in willpower, or lack of same?
Claiming there has been an increase in firepower might be justified, if one looks at the improved performance of ammunition in recent decades, after all, modern JHP bullets do perform significantly better than FMJ or lead, for anti-personnel purposes.
As to the proliferation of "high capacity" autoloaders, there are a few reasons, some not already discussed. Like Hollywood, for one. Take a look at popular entertainment of the last 50 years and you will find some clues. Prior to, and for a couple of decades after WW II, the most common "action" movies (and later TV shows) were westerns. Lots of guns and shooting in those pictures (more so than in the actual old west), but no machine guns or autoloading pistols. Move into the 60s and you see a shift to more "urban" drama, and the westerns fade. Car chases, machineguns and autopistols and other visually dramatic action (explosions, etc.) gradually become more and more common. Keep moving forward in time and what you get is more and more of the same, in a never ending effort to be more dramatic, in order to capture the public interest, and by so doing, make money.
There was a time when the only place in movies/tv that one saw a lot of automatic weapons was war movies. That has changed. For a couple of decades now (at least), the people making movies/tv have used a virtual formula of having nearly all the bad guys being armed with machineguns/assault rifles, and while they shoot up a whole lot of the surroundings, they never seem to be able to hit the hero, who then takes out the evil minions one, two, or three at a time, often with casual ease, using a (often large) handgun, or sometimes some of the bad guys guns, until reaching the head villian, where a shootout, then a physical fight occurs. The hero gets beaten for a while, but triumphs in the end. There are dozens of movies and TV shows that use some variation of this basic formula.
Auto pistols are not as dramatic as machine guns, but they are much more visually dramatic than revolvers. Slides going back and forth, magazines being inserted, brass flying, all a lot more interesting to watch than revolvers. Constant exposure on the screen does have an effect on attitudes. The "coolness" factor.
Another not yet mentioned factor in why we have so many autopistols running around today is the simple fact that in the last couple of decades a lot more people have had more money to spend than they did back in the 20s and 30s. And that includes Law Enforcement. Law Enforcement got a huge boost to their pocketbooks due to the war on drugs. And some of their new found money goes for guns. More people with money to buy autopistols, more cops buying autopistols, more autopistol designs made to take up the market, Hollywood blazing away, shooting nearly as much in an average day of "entertainment" as our soldiers did during the Normandy invasion, it all adds up. It wasn't that revolvers didn't work any more, or that they were any less effective, it was (as much as anything) a perception issue.
And now we get to the real heart of the matter. Why was it percieved that the cops were "outgunned", and why is it percieved that there is more "firepower" on the streets today? Because so many people (criminals, mostly) are willing to shoot! And shoot often, with little or no reason, other than they can, and they want to. And why? Maybe it might have something to do with a couple of generations virtually being trained since birth by a TV screen showing them that using a gun is the solution to every problem. Maybe it has something to do with the fact that back in the bad old gangster days of the 20s and 30s, that when killers were caught and convicted, they got the chair, or the gas chamber (and it didn't take 20+ years to be carried out) or they "went up the river" for a long time. And they stayed there!
Maybe it has something to do with so many people not giving a crap what happens to them beyond the moment. Maybe it is all these things and more, but the end result is that there is a perception that there is more "firepower" on the street.
But, if there actuall is more firepower on the street, it is being used very strangely. The correlation ought to be that the increased firepower results in tremendously increased body count, and the crime statistics for the past few decades just do not bear this out. There are, and have been, individual instances with high body counts, and the media makes endless money playing these statistically rare happenings for all they can get, both in dollars, and to further their ideals of societial change (like banning guns).
School shooting, and other rampage killers are big news, and the body counts are horrifying, to be sure, but these things are not common, not the way the media portrays them to be. With well over a couple of hundred million people in the country, they can't be, or we would be up to our eyeballs in bodies, every day, day in and day out. Severe "gun violence" (and I personally detest that term, making it sound as if the guns are the cause) is a localized phenomenon. Predominant in some areas, but virtually non existant in others. Yet certain members of the media and certain politicians make it sound as if is equally bad everywhere. They profit from our fear. Any wonder they are constantly trying to increase it?