Disk capacity unchanged after deleting 21 GB MacPorts

[list_email at icloud.com]

As a first step in re-installing MacPorts (long story), I ran

$ sudo port -fp uninstall installed

according to the instructions at 

https://guide.macports.org/#installing.macports.uninstalling

Before uninstalling, the Finder indicated that /opt/local contained 21 GB. After, /opt/local was nearly empty, as expected. I completed the steps indicated to complete the uninstallation.

I happened to check the “Used” quantity, as indicated by Finder on Get Info on my boot volume (which contained /opt/local) before uninstalling, and again after uninstalling. I expected to see this quantity reduced by 21 GB. But there was no change!

Why was the “Used” number unchanged after deleting 21 GB?

Thanks.

Jerry