Gross subject matter alert, up front.
RN bullets and mid-caliber chamberings lost favor in LE circles when the rules of engagement changed after WWII. Back in those days, it was considered proper and sporting to fire upon fleeing suspected felons without much regard for their status as "armed' or not. Police- and citizen-fired bullets were as much "marking pellets" as defensive tools--maybe more the former than the latter. The rationale was that said suspected felon might absorb one or more of those pellets and eventually come to the attention of either the medicos or the undertaker, who by law were and are required to report such events to the gendarmerie. Imagine a time that placed at least equal emphasis upon identifying a crime suspect positively and causing him/her to answer for his/her misdeeds, compared to today's standard of assuring that all possible steps were taken to assure a predator's comfort and well-being prior to assessing his/her guilt. It was a fine country, back in the day.
But I digress, as usual. After WWII, social mores began to frown upon those who projected finality upon otherwise well-deserving recipients unless said projector was also under quasi-fatal duress. IOW, the bad guys are generally COMING AT YOU or at close quarters, and not retiring from the field. The shortcomings of light-tackle angling and streamlined bullet forms became readily apparent. Per bullets fired, a lot more cops and citizens started getting shot than crooks, unlike times past. That would not do--hence the push for fatter and flatter bullets, with expansion being rated a good thing. On and on it goes.