This is a cynical charge exploiting people dropping off pax & taking 5 mins to do so. I don't think that it clogs up the forecourt either. At least not at a fairly quiet airport like Bournemouth.
I suppose that if the airport doesn't get the passenger with a dropping off charge it will get the equivalent amount from some other charge; possibly equally as frivolous. So, we end up paying anyway. either way, the passenger loses out.