Adding symlink to /usr/bin

I'm trying to add python3 to my path by adding a symlink but it's erroring and I'm not sure why. /usr/bin $ sudo su sh-3.2# ln -s /Library/Frameworks/Python.framework/Versions/3.7/bin/python3 /usr/bin/python3 ln: /usr/bin/python3: Operation not permitted sh-3.2# whoami root sh-3.2# ls -la | head -n 2 total 139064 drwxr-xr-x 977 root wheel 31264 24 Jul 2018 . *** Edit *** I have symlinked from /usr/local/bin/python3 so that's fine.