I don't see the point in just reducing fares, as you're able to offer something that can encourage more travel (off peak) to get bigger savings. If all fares were simply cheaper, there's no feeling of wanting to get the most from the card.
It's all psychological I'm sure, but if someone invests in a Network Railcard or Family Railcard, they've got more incentive to now travel by train. That's the benefit of the railcard, and why if you had a national railcard at a higher price - you'd perhaps get more people to use the train and, gradually, see that it isn't all bad (most of the time).
I imagine the free Daily Mail family railcard given each year probably does quite well. It's quite amazing the paper does this given its anti-railway stance on most articles!