That was their stated reason (and I've read their tests and agree with them for the most part). However I have to believe the almighty dollar played a significant role as well.The FBI determined in 2014 that modern 9mm projectiles were as effective as any handgun round against human targets, agents were able to shoot faster more accurate strings of rounds with 9mm and 9mm pistols held more rounds for the same size pistol than larger calibers.
Therefore they switched to 9mm and recommended 9mm to other law enforcement agencies. A lot of agencies followed suit and made the change to 9mm. Making used G22s the best value gun in the world at the moment.