I'd agree with ATLDave's assessments. When the crux of succeeding in using a defensive sidearm is well understood to be making fast decently accurate hits, repeatedly, when it is understood that once you've managed to drive that bullet through the bad guy there's no benefit to a lot of excess energy, and when it is demonstrable to anyone with a timer that more recoil slows down everybody, no matter how good a shooter you are, it doesn't make much sense to push 10mm, .41 Mag, or the various other high energy handgun rounds as combat or police (or self-defense) cartridges.
Add in the fact that the need, or ability, or effectiveness of shooting through heavy steel automobile parts or other barriers has been largely set aside as a crucial factor.
Call it behavioral economics, or just "too much of a good thing." 9mm is fine, .45ACP is fine, .40 S&W is fine. Lamenting that the FBI didn't really put in the effort to train officers to be good with that heavy load is probably wrong. It seems like that was one thing they got right.