It would also depend on whether the person in question had brought their Freedom pass with them, if they were just popping out locally.
I can see how it would seem like the most sensible thing would be to open the railway bridge to the public, but I can also imagine there would be a lot of health and safety rules Network Rail would have to address. Presumably there will be extra passengers using the bridge in both directions with the subway out of action. If you add general pedestrians, will Network Rail (or whoever are responsible, I lose track) be responsible for their safety too? I'm not saying there would be a problem, and there may be willingness in principle, but it might not be as simple as opening the gates and saying come one, come all. To imply that the station staff are just be obdurate is probably not very fair.