Why does data remain after disk erase and factory reset - macOS Monterey

I've tried to erase and factory reset my MacBook, using *Erase All Content and Settings in System Preferences*. However, after completing the operation, and configuring the MacBook again, I can find the previous accounts in Mail, passwords of the wifi and all the previous settings of the last configuration. Why does this happen? I don't have any backup on iCloud, I've checked many times. Anyway I choose to configure as a new MacBook. How can I be sure the MacBook has been formatted if I find all this information after Erasing All Content? I have a MacBook with T2 chip.