Unfortunately public transport and esp. railway transport is not a 100% free market, there are a lot of natural monopolies in this space that need to be regulat

Unfortunately public transport and esp. railway transport is not a 100% free market, there are a lot of natural monopolies in this space that need to be regulated. For example what stops Eurostar from pricing their tickets by looking at airline ones (it's what they are apparently doing)? Nothing because Eurostar is a monopolist for some important destination pairs like Paris - London.