I am not a local transport planner and, based on what goes on locally to me, I would be very ashamed if I were.
I suspect that local businesses may contribute towards the cost of the Park and Ride in the hope that it will make the town a more accessible place to visit to those who live some way away. This would be good for business.
The purpose is to discourage cars from entering the town centre. Pedestrians turning up for the Ride are presumably assumed to be not going to clog the town centre with traffic and therefore do not need a cost incentive to use the facility. And they would presumably shop in the town anyway, since they live so close to it. Charging them more would also help to keep the service more available to those for whom it as intended. However, the overall result is somewhat bizarre.