I think they are reaching out to GMB account owners because so many do not know what's going on.
I think of small businesses who get the "You are not on the first page of Google" calls and pay small amounts of money for ad campaigns that mostly do nothing. It's an easy audience to confuse with a bit of babble. Very few senators are getting letters saying, "Please pass SB 2992," so if Google gets a small number of companies to write saying, "Please don't," it will be hard to get a 50+1 vote on it.