Until now, deleting an account removed every row about you from the database and left the files you had generated — images, videos, voice and music — sitting in storage at addresses that still worked. The privacy policy promised erasure; the button did most of it.
Delete Account now erases your stored files first, across every bucket that holds them, and only then removes the account. Each deletion writes a small record — when, how many objects, and whether any bucket failed — holding nothing that identifies you, so we can prove the erasure happened without keeping what was erased.
The files left behind by accounts deleted before this change are being removed separately, through the same mechanism.