What is the rationale for fighting a unified system? A unified system would make it easier to travel by train, which should in theory encourage people to do so

What is the rationale for fighting a unified system? A unified system would make it easier to travel by train, which should in theory encourage people to do so more. Is this a problem of the operators within each country not wanting to be unified with each other because then they'd have to compete more directly? Or is this actually the operators between countries fighting over it for some reason?