Earlier quoted context omitted.
This is the explanation that makes the most sense to me. I'm not sure what the fix is - having multiple companies sharing the same track seem dubious but maybe that's answer. Either that or let a bunch of companies put down redundant lines.
EU intervention. It worked for getting rid of roaming prices for mobile phone carriers in Europe, and that also requires cooperation between different carriers. Why wouldn't something like that be possible for rail?
The problem is lack of demand. The article posits there is huge untapped demand for night trains but there isn't. Rail companies can and do run services on each others tracks but rail lines are frequently at capacity, timetabling wise, so it's not always easy to just drop in and run extra trains in the same way many airports have free slots for extra planes. And of course airlines are still mostly national too.
Indeed it's best kept away from the EU. It has a habit of suspending transport and trading rights as part of unrelated political disputes with its neighbors in order to pressure them to obey Brussels. If you want train connections to be mysteriously severed because of some dispute with the UK or Switzerland over fishing or trade unions then asking the EU to organise it is the right way to go. If you'd like train timetables to be set taking into account what the railways can do, leave it to the private sector and get governments out of the way.