And why should they? I don't know where my browser cache is either. Or my rows in my sqlite database. Or the system clock configuration. Actually I do know: They're stored on the hard drive.
Files aren't physical.
Files aren't physical.
This makes it a pain where you want to have a custom configuration. Like moving the cache to a ramdisk. My NVME disk is plenty fast, but rarely I want my browser cache to persist across a reboot. It's a pain to move the cache to /tmp/firefox-cache as an example (/tmp is a ramdisk on my laptop). Also a pain to backup profiles.
import the images from both libraries (https://support.apple.com/en-us/119920)
View > Utilities > Duplicates
or use jdupes or czkawka on both directories.