http://www.transportfocus.org.uk/help/rail-complaints
extract from 'Taking rail complaints further' said:
Have you complained to the train company?
If not, you need to complain directly to the train company involved (see
our advice on how to do this).
Basically Transport Focus will not look at your case if you've not contacted the train company.
As for why, I guess because many people (not savvy users of this forum) will bombard them with trivial complaints/queries that could be rectified by the Train Company.
Unfortunately, as we know, there are certain complaints that the Train Company will not resolve satisfactorily willingly and it's a waste of time complaining to the Train Company and it would be nice if 'advanced' users could bypass that step. However that's not the way it is, so we do have to contact the TOC.
It's a bit annoying, but I can understand why they make us do this.
However as far as I am concerned, if a TOC has given a response and you're unhappy with it, there is no point going back to them, and I would go to Transport Focus at that point.
Many people do not complain because the amount of time you end up wasting dealing with stubborn customer service departments is rarely worth it in monetary terms, so the only reason is to prove a point and help others in future.
I could list dozens of complaints* I'd like to see resolved and I'd waste a lot of time if I tried to properly pursue them.
I am glad some people are prepared to put the time and effort in, but I can also see why many people don't want to spend hours doing this.
(* by that I don't necessarily mean incidents I have directly been involved in, but things other people have experienced, and will experience in future if they make certain purchases/journeys)