Well it was always available to tens of thousands of people with no confidentiality expressed or implied. They just tried to keep it hidden to twist your arm to employ them. Private sales don't make it into housesigma fwiw (and I assume not into real-estate databases either?). Sell privately and it makes it a lot harder for people to figure it out. It also makes it a lot harder to get a bidding war that drives your price to the moon. How much is your privacy worth? An old farmhouse on 20 acres listed for 1.5 on Georgian Bay and ended up with nine people fighting and went for 2.6. I have no idea what the "right" price is.
Besides, even if they know what you sold your house for, they don't know your finances. Maybe you have a gambling problem or went all in on a leveraged bet on diamond hands and selling the house gets you back to zero.