We all know that if the advice is changed it will lead to a ’free for all’ with service over capacity.
There appears to be a misunderstanding.
To be clear, the OP was asking for people how rail travel could be encouraged
post-Covid19.
As far as I am aware, no-one is saying that it should be encouraged
now, though people are - quite understandably - pointing out that train companies should not be misleading people on what the actual Government advice says.
As I said before, this is arguably
not within the remit of this thread, though I certainly can see how it's
linked, from the point of view that actively discouraging public transport right now (and going well beyond what the Government advice says) makes it harder to encourage people to travel when the time comes to do that. Clearly there is also likely to be an intermediate period, where travel is neither discouraged nor encouraged.