They do not offer cheap fares to be nice to the travellers. Putting up prices at weekends will cost the railways passengers and lose them money. I assume that the absence of discounted fares is due to technical factors and uncertainties over the short term as
@staffsblue has already pointed out.
Once things get back to something approaching normality, I expect the saver prices to be restored. Apart from anything else a number of people have shifted from rail to private car during the pandemic. The railways will want to win back this trade. I suppose it will depend if there is a big backlog if maintenance works with weekend closures.
We normally travel from Edinburgh by rail for match days. For the Everton match, the West Coast line was shut north of Carlisle for engineering works and the price to travel East Coast to Manchester via York was ridiculously high. So we ended up driving down and staying overnight.