This report suggests that the RCMP found the best 9mm loads available at the time to be "good enough". That is to say, at least as good as the old .38 Special +P 158 grain hollow point. Also, I suspect that ammunition commonality with the MP5, as mentioned in the report, may have been a factor.
...Not really a big factor although it was a consideration, as at the time the of the 5946 issuance, ALMOST the only ones using the MP5 were ERT, and they also used the HK as their side arm when deployed as ERT Mbrs...It really wasn't a case of being good enough, but rather a case of choosing the best load/round that was then available.....As to the final RCMP issued load for the 38SPL, it was the much vaunted "FBI load" with velocities in the low end of the 357 Magnum range, and the Semi-Wadcutter offered excellent" stopping power" while still being controllable....It should be borne in mind that the older (low numbered, C"Prefixed) Model 10s were deemed UNSAFE with the higher pressures of the+P round,and nobody at the time, ever questioned the 357 Mag performance in the Police role......David K