That's not quite correct IIRC. The Department for Transport limits how many services and coaches are allowed on each route. Which is why you get 4-5 car Voyagers on CrossCountry on standing room only services.
I'd like to know why. All long distance journeys need at least 8 carriages. (and not two fours stuck together either). More coaches needed on the Sheffield to Manchester line also needed.
The fundamental problem is nationalisation. There are very few passenger railways worldwide that operate at a profit. The Hong Kong MTR does because it carries an exceptionally high number of passengers as a ratio to the size of the infrastructure. France and Italy utilises their infrastructure to move goods which helps subsidise the passenger carriage. Passenger rail travel is a public service and in the main cannot be profitable without subsidisation. Privatisation doesn’t invest sufficient in rolling stock or infrastructure (forget HS2). To carry out maintenance on the East Coast mainline can take 12 months to obtain a possession. That’s because there aren’t viable alternative routes or “passing loops”. In HK it took less than a week to obtain a possession. It will not get better whilst our rail systems are in the hands of the private sector.
How does ticketing work? Thought about taking the train to Leeds, outbound OK, I knew which specific train I wanted to get on, return I had to book a specific train back, no obvious option for an open return. As I didn't know how long I'd be chalked F on it and drove to Stourton P&R, £4 return bus into the city.
On trainline and northern railway apps. They offer return or open return selection. (Little difference in price on short journeys. Note peak and off peak times different on some operators. . Peak generally on northern rail 6:30am - 9:30am and between 4:30 pm - 7 pm. ) On the preferences. As do ticket machines and booking offices. If you buy on train the price shoots up.