osx 10.11.6: SDcard reader
The Pi likely formatted the filesystem as a Linux ext4 filesystem.  

Type cat /etc/fstab and check the filesystem type of your / partition (look to see if it says ext4).

You can enable ssh on the Pi and use scp to copy the files across to your mac.  You can use sudo raspi-config on the Pi, go into the "Interfacing Options" menu and enable ssh.

You could install ext4 filesystem support on the Mac to make it possible to mount the sdcard.  To do this, you would install FUSE for macOS and make sure you install the ext4fuse filesystem handler.

There are numerous articles that walk through the steps required.  Here is just one example:  https://www.jeffgeerling.com/blog/2017/mount-raspberry-pi-sd-card-on-mac-read-only-osxfuse-and-ext4fuse