Basically, BEVs need to have huge batteries to sell well. Not because the consumer is actually using this huge battery to its full extent, but because otherwise the consumer will not buy the car due to range anxiety. This huge battery, of which maybe 1/4 or 1/3 is used throughout a day, is a huge inefficiency to manufacture and adds significantly to the CO2 footprint of BEVs. For a lot of people it might therefore make more sense to have a PHEV with a battery big enough for one day of driving, and a range extender, which ideally would not be used in day to day driving. The range extender is an ICE engine or gas turbine, which is made of more common materials. In the future it might even make sense to combine PHEV with synthetic fuels.
The argument I heard against this is that people with PHEVs ignore the plug-in functionality and drive it on gas the whole time. But while this might be true, it does not counter the technical argument above. It is a completely other problem.