Switzerland has for decades been investing high levels of money in improving the infrastructure and ensuring there is sufficient capacity. Ultimately because this is what the people want.
The network was already mostly electrified by the 1950s. There are several major projects under construction right now that will alleviate pinch points or add capacity. Recently new base tunnels were opened under the Alps. Plus countless less spectacular but equally necessary projects involving for example re-alignment of routes, new stations, new tunnels, even entirely new lines. I don't think there has been a time since the 1980s that there have not been several major projects under construction simultaneously. And there is plenty more in the pipeline. Of course all this costs money, and that money can only be spent because people support it being spent. And they only support it being spent because they use the trains and see the advantages they offer.
To see the opposite there are plenty of African and South American countries where governments took ownership of the railroads that had hitherto been run somehow successfully (when one takes into account the circumstances), and then through general disinterest allowed things to deteriorate to the point that there was hardly anything left at all.
An incompetent corporation will sooner or later have to face the wrath of its shareholders or face bankruptcy. An incompetent government agency protected by a rut of indifference can wriggle on seemingly forever. Especially if the government always has more pressing problems to attend to.
Japan is an example of a country where the railroads are essentially privately owned and still manage to perform to a very high standard.
The differentiating factor is thus not who owns the railroad but what are the public and policy demands placed on it.
