For multiple reason:
- These companies make absurdly huge profit that could be reinvested into the network to improve the network for everybody (electrification, passenger transport). And these are not some complex tech companies that the government couldn't operate.
- These companies are blocking passenger travel and don't care that they are doing it, all other approaches to prevent this have failed. With the current structure there is no change for the US ever to develop a serious passenger rail infrastructure, either inter-city, regional or S-Bahn style. Many local government and states might want to do more train stuff but currently don't feel empowered to do so any trying is often not even worth it.
- They are removing anything not absurdly profitable, shifting things from rail to trucks. And then trucks use government funded road and highway infrastructure instead. Its just bad intensives.
- Current companies have a bad track record and there are way to many derailments, and this is serious strategic concern for logistics that the government should really take better care off.
Just for reference, with the current profit of these companies, the US could easily executed a systematic program of electrification, track and signaling upgrades. Vastly improving both the amount of cargo that can be transported and the passenger that can be transported, and doing so in a much more substantial way.
While trains are energy efficient, and its better then trucks, currently they use very dirty locos with no plan of changing it (some mild greenwashing but nothing real). Some of these train companies are literally some of the largest individual users of fossil fuels (behind things like DoD) and no plan for change anytime soon.
It would also make transporting cargo from city-to-city easier if these cities are currently in the domain of one of the competitor companies. This is a real problem for shipping.
If the US wants to seriously drive modal share of cargo and passenger transport to green energy efficient trains, its the only way I can see it gone work.