The bus service is going to change in 3 weeks? I don't think so.

If it is likely to change, the organizers are in a better position to know than Traveline, which only gives current schedules. You don't want to plan travel to a festival only to find that your transport to it has been taken out of service by the time you go (that did actually happen to me once).

Car drivers get all the information they need on that site. Are you implying that they're all too dim to work out a route given a map reference? - maybe they are.

Usually this kind of ignorance is simply because the organizers regard anyone who doesn't have a car as belonging to an inferior caste they want to keep out.