I doubt that that attitude is coming from Southern management as some kind of warped directive specifically designed to p-off disabled people. However, I can imagine that it could be the result of having a uninterested and disengaged workforce, who simply don't give a toss anymore, brought about by the ridiculous dispute that has been ongoing for some time.
Anyone who has ever tried to effect change in an underperforming organisation, especially a public or quasi public sector setting such as the railways, will tell you that changing organisational culture is the biggest blocker of all.
An environment where the "not my job/problem mate" or pointing to the "rulebook" is the default, blaming or trying to find reasons to blame customers for their own misfortune to cover up shortcomings and a management culture which allows that environment to develop or be sustained is generally the reason for it.
If you choose to work in a public service environment and have any pride in your work at all, you don't allow your customers, particularly those who are vulnerable through age or disability to suffer simply because you're having an ongoing dispute with the Boss.....like I say, this is about basic human nature.
If that's too much to ask, you probably need to ask yourself if you're in the right job.