Why Doesn’t Disk Cleanup Delete All Files?
After you’ve used Disk Cleanup, you probably expect every temporary file to be completely deleted, but that’s not actually the case. Files are only deleted if they are older than 7 days old, but you can tweak that number to something else.

Since these files are often being used by applications, Windows doesn’t know whether a particular file can be deleted, so Disk Cleanup only cleans up files that are older than 7 days, which is a safe guess—most people probably don’t have an application open for more than a week, especially since Microsoft makes you reboot nearly every Tuesday, right?

If you’re one of those people that reboots your PC every day, you can probably change the Disk Cleanup value down to something lower, like 2 days.