Because even though one line was added, two were deleted and that's confusing when reviewing.

Also if you would like to sort them, you would have to manually add the missing comma, because the there will be a syntax error if the last item will move in the middle.. (if someone will mention that these things are handled by Prettier 😃)

More reasons can be found here: https://medium.com/@nikgraf/why-you-should-enforce-dangling-commas-for-multiline-statements-d034c98e36f8