They are in some commuter markets, arguably inter-city markets, especially if you don't own a car. In reality some services are the only game in town.
The Southern Rail dispute is a good example.
Here was have an intransigent TOC v intransigent Union, each side knowing at various levels they have a captive market.
This sort of dispute could never take place in the energy, IT, telecoms, car, breakfast cereal, horse grooming markets, because consumers could switch to alternative services, employees to alternative employers, there is a limit of what can be realistically charged. If the market is working correctly, once it settles, profits should be relatively thin.
I accept SR has some fares regulated because of this.