The dynamics of air transport are very different though. Air transport involves hubs with carriers from all over the world flying into them. Rail lines typically involves one or two companies having access to a given piece of rail infrastructure (generally with natural or state-guaranteed monopolies on particular routes) so vertical integration makes a lot more sense, especially compared with a model where operating companies don't have the flexibility to push forward upgrade timetables they think are commercially necessary, but do get to capture profit windfalls from public investment.