Can you imagine bus companies charging customers for using their bus stops, or railway companies charging for using their stations?
Actually, in BOTH cases, those fees DO exist, they are just not displayed as part of the ticket.
My contacts in the rail industry tell me that the average station user charge is around 50p-£1 for a large London terminus. As with airports, stations can make good money on retail and catering, so the user fee is kept below a level where it would be noticed, or where people would alight at London Hahn (Watford Junction) and continue by tube.
Outside the main city centres, you will also see - guess what - lots of car parks these days, from which the train companies are making good money from long stay (or short stay by airport standards) parking.
No need to top it up with a drop off charge, people would just nip around the corner, which they can't do at airports.
As for bus stations, these tend to be provided by local authorities, but there is stilll a usage fee, such that some local bus companies (eg Stagecoach here) won't use them, Likewise, "Megabus" use the Canon Park Shopping Ctr near Warwick Uni, not the city centre for a stop - although that no doubt is better for scheduling too.
In Leeds, there is even a big billboard by the Megabus stop, advertising that National Express use the "proper" bus station.
In our post-privatisation transport world, there is rarely seamless linkage between transport and station (including airport) operator, so some sort of charging method is always going to exist, whether public or not.