I think they’re using the robot voices to try to save the human scammers a little time.
I’ve been getting the robot voices on voicemails with all kinds of scams (the “you owe the IRS money and we are going to put you in the jail” scam, and the “we suspend your Social Security number for suspicious activity” and the “we have detected virus on your computer and you must call us at Microsoft tech support” and so on).
