Why the difference in size of guest disk?

Just did a cleanup in windows, and the space went from 64gb to 45gb (removed old backups, downloaded files, cleared recycle bin, etc.). Parallels reclaimed 3gb not the nearly 20 gb that windows did.

Why is there such a discrepancy between the used / free space from windows vs parallels?
Parallels Version 18.3.1 (53614), MacBook Air M2, Windows 11 Pro