I don't know why, but as a strategy, you should always (also) look at the national railway's own websites.
And a small anecdote:
Last year I travelled through Sweden with a pass and when planning that trip I came across this message from the SJ (Swedish railways) which I found so funny that I took a screenshot and saved it (it was probably auto-translated):
The journey is preliminary
we release tickets once the planning is complete and we know how the trains will be able to run.
Check back later or choose another journey.
Note that this was a message on 23rd of June, for a journey due to take place on 15 August (just 7 weeks later).
I cannot plan a journey which such non-information so booked the Snälltåget instead and have never regretted that.