Probably because APFS runs on everything from the Apple Watch to the Mac Pro and everything in between. You probably don’t want your phone or watch de-duping s

Probably because APFS runs on everything from the Apple Watch to the Mac Pro and everything in between. You probably don’t want your phone or watch de-duping stuff. There are tons of knobs you can tweak in macOS but Apple has always been pretty conservative when it comes to what should be default behavior for the vast majority of their users. Certainly when you duplicate a file using the Finder or use cp -c at the command line, the Copy-on-Write functionality is being used; most users don’t need to know that.