Fashion changes. Technology advances.
Whether the movement to semi-autos is a result of fashion or technology is a judgement call.
Police and security videos notwithstanding, most CITIZEN involved shootings still fall into the 1 to 3 shot count.
However, given equal cartridge count, a flat-sided semi-auto is generally easier to conceal than a revolver, with its cylinder bulge.
The standard advice when selecting a firearm is to choose a bullet and energy level right for the job, then select a cartridge that delivers that bullet with that velocity. Lastly, make a list of all firearms that chamber that cartridge. (This advice came from a rifleman/hunter, not armed citizen, but with certain modifications, it is where I always start when selecting a handgun.)
Between 9mm and 38 special (roughly comparable self-defense rounds), I would expect the 9mm to be my choice.
Between a compact .40 S&W and revolver, there is no comparable revolver cartridge unless you get a 5-shot .40 or move up to the 44 special. How many choices do you have in concealable 44 specials other than Charter Arms? Of course, you could compare the .357 Mag or .38 +p, but penetration is a concern.
Between a .45 Semi-auto and CONCEALABLE revolvers, there are simply no comparables (that I know of) unless you want to suggest the 44 special of which there is the afore-mentioned paucity of choices.
Choosing an action type complicates my selection decision tree, especially for social (rather than hunting) situations.
So, why do I most often carry a 5-shot revolver? For the most part, being a citizen with no particular duty to go into situations known to be dangerous, if I felt the need for more than 5 or 6 rounds, I would re-think my need to be in that location at all. If I REALLY needed to be there, I would be more likely to bring friends.
One example. I was helping a lady out of an abusive relationship and we went to collect her clothes. Her husband had agreed over the telephone to not be there at the appointed time. We took two cars. She and I were in one and my friend in another, who stood off some distance, just in case.
Point: The arms you carry are only one element of your tactics.
Lost Sheep