There is certainly a perception in some quarters that Their Taxpayers are willing to subsidise the railways, which are therefore Nice, while Our Taxpayers flogged the railways off for profit, thereby making them Nasty. This view is incorrect in a number of ways, but is correct in others, and makes for a simple narrative.
The average would-be rail traveller is wary of complexity because they have a perception that they'll find themselves with a ticket they can't use for the journey they intend to make.
Advance tickets are easy to understand, because they work like airline tickets. You sit in this seat on that train, and no other, and all is well with the world. For a lot of passengers, that's great... provided that they're able to get on the booked train.
Anytime tickets are easy to understand, because you can use them on any train, and don't need to worry about restrictions. Unless you do, thanks to recent events which won't be helping the perception of complexity. Off Peak is confusing, since the times are wildly inconsistent by route and operator; Super Off Peak is even worse.
The fact that ticket splitting works clearly isn't a sign of simplicity. And when they do come unstuck, through no fault of their own, the perception will be that the rail industry has sold them a complicated ticket that they can't use, rather than a simple one that they can.
Yes, you and I know it's cheaper because of that complexity. But the average punter sees a ticket from A to B for £20, and one from B to C for £30, all on the same train, and reasonably concludes that £50 is the amount of money the railway wants for that journey.