The entire basis for this is the assumption that goods are being transported using fossil fuels. If we transport the goods using electric trucks suddenly plastic starts to look much, much worse than paper or even glass.
Aluminum is much better all around so I'm not sure why it's lumped into everything else. It's basically infinitely recyclable and you don't have to use natural gas or propane to heat it up to the melting point for forming/extrusion. There's basically an infinite amount of ways to heat things up; even to really high temperatures.