You still seem to miss the point about railroads serving industrial customers. A city may be served by five different Class I railroads, but that doesn't mean all of them can access every industrial customer in the city. For example, the major Honda auto plant in Marysville, Ohio is served by CSX Railways. Period. That's it. The railroads invest a ton of money in building the infrastructure to serve large customers like this, and it's not in their best interests to invest in fixed assets like this if they have to deal with competing railroads directly accessing the same customer.
P.S. — I see this issue mainly from the perspective of the railroad customer, not the government.
Consider all the time that Conrail operated without profit for that quarter-century of its existence.
Comparing today’s monopolistic crony-capitalist setup with the multiple-player past (which was destroyed, as I said, by regulation and taxation as well as government support of the competing modes’ infrastructure) is a canard. It is more like one step away from bringing back a larger Conrail if the government so wished.