The UK's rail "privatisation" has always been bizarre, for practical reasons.
* Because rail is vital national infrastructure, important to keeping congestion down, and needs to be accessible even to poor people, every train operator receives government subsidies.
* So travellers can buy tickets for a complex four-train itinerary and large stations can have multiple operators sharing platforms, much of the ticketing system (including the main types of ticket on offer) is centrally controlled.
* Because it would be nigh-impossible to have multiple companies trains with different prices (or different on-time performance) operating on the same route, each route is essentially a monopoly †.
* To prevent price-gouging of commuters on monopoly services, the rate of increase of ticket prices is capped by government. (And yet despite the subsidies and price caps, some train tickets remain absurdly expensive)
* It would be absurd for a company losing a rail franchise to get stuck with a bunch of trains they no longer need, or a bunch of employees in the wrong part of the country they have to fire. So when a rail franchise changes hands, the trains, drivers, stations, and station staff move with it.
* Any long-term investments in things like new trains won't pay off in the duration of a single rail franchise - so they have to be agreed with the government upfront.
* Rail workers are represented by powerful unions, and industrial disputes tank the train operators' performance numbers, so operators can't control their staffing costs - they can only wait out a long industrial dispute with government backing.
* To prevent rural communities losing their rail service (or having it reduced to unusable levels) the government tells the franchisee where the trains must stop, and how often.
* Because tracks and signals all have to be maintained to the same national standards, and often multiple trains will use the same tracks, the train operators don't own the tracks or signalling equipment. So they can't upgrade track for automation or to run more/faster/more reliable services.
* Because re-tendering a franchise is very time-consuming, train operators who under-perform are seldom replaced or punished (except by making less money than they hoped they would)
All of this means the train operators are boxed in on every side - Can't run more trains, can't run fewer trains, can't raise prices, can't change pricing models, can't embrace tech like driverless trains, can't cut staff. Their only powers seem to be choosing the train's colour scheme, taking the blame for poor performance, and giving some bigwig a fat salary.
Given that the trains have always been de-facto under state control, making that true de-jure makes sense.
† Except for one or two services like london-to-birmingham, and competition from cars and teleworking.