Train tickets are priced to maximise profits for shareholders. For a lot of tickets there's a maximum amount they're allowed to raise them by each year, and you better believe they do exactly that.

They're slowly being renationalised when their contracts run out, which is a start.

A good benchmark for pricing should be "two people taking a train should cost about the same as it would to drive in a car". It's nowhere near that. For most long UK journeys it's cheaper to fly to another European country and fly back to the destination than it is to take a train.