Saw the American handgunner stating.
I told my father this (who has always been a .45 man) and his always says "I think they pick that cause the women can’t shoot 45 ACP." he said that before when I bought my XD 40 SC. I looked around and seems to me the reason they switched was because they wanted more power from the 9mm frame, and the 40 fit thatthe most popular handgun calibers used by that state police in 49 states are (HI has no state police agency, hence only 49 states):
.40 S&W - AL, AK, AZ, CA, CO, CT, IL, IO, KY, LA, MD, MA, MI, MN, MS, MO, NE, NV, ND, OH, OR, UT, VT, WA, WI, WY (26)
.357 Sig - DE, MT, NM, NC, OK, RI, SD, TN, TX, VA (10)
.45 ACP - AR, ID, KS, ME, NH, WV (6)
.45 GAP - FL, GA, NY, PA, SC (5)
9mm - IN, NJ (2)