`sudoers` file resets with every macOS update
Modifying most of the files in /etc leaves you open to them being replaced during OS updates. That's why most of the ones you usually need to change have the facility to add files to a directory instead.
If you look in /etc you will see a directory called sudoers.d and the last line of the sudoers file is #includedir /private/etc/sudoers.d so any file of commands you put into the directory will be read. Files in the directory will not be overwritten when you update.
You may notice directories with similar names in /etc that fill the same function for other parts of the system.