The entire article and the decisions made can be summed up in your last sentence..40 vs 9mm you lose capacity, more recoil and the ballistics on them are similar.
FBI did a study and they went from .40 to 9mm as did most of police departments around the country.
here is a article :
https://www.policemag.com/341954/9mm-vs-40-caliber
also 9mm is cheaper