We privatized Americas rail system for the same reason we privatized everything: privatized profits and socialize losses.
We've even been giving the owners of the rails money that they're supposed to be using to maintain them, and for decades they just dont it.
Then we have massive toxic spill accidents because they didn't maintain the rail or cars and they don't follow guidelines.
And so they get fined, but that's just a cost of business as long as insurance pays out.
There's no logical reason for critical infrastructure to be privately owned.