It is not intended as a 'normal' ticket but is a promotional fare and, in this case, looks to be promoting the first anniversary of St Pancras International hence why the ticket is only available for just over a month.
In exactly the same way NXEC have £5 promotional fares for their birthday at present they are not directly shown as doing so on their home page (and presumably not at stations either).
The fact is, TOCs run a business and try to maximise turnover. Some people have to be priced off the railways (hence the peak time fares), and so they cannot be too low (TOCs - especially FCC already have severe overcrowding issues and do not want to add to that). Too high will stop people using their services altogether and then they generate no revenue.
Having this ticket (albeit temporarily) will encourage people who might not have used the train to use it (if they are aware of the promotion) and the Super Off Peak aspect is to fill up lighter used services.
But wait - you think to yourself that then, FCC will be increasing their revenue by doing this. The problem is they want more profit so cannot afford for the whole train load to be having this sort of ticket hence the advertising about it is rather low. And then those who do get the ticket for their first journey on the train will turn up again after Christmas and then be amazed the ticket is no more (probably then to have to pay the higher fare)...
