Unlike in Europe, where rail maintenance is heavily subsidised by the government, in the US it is paid for by the private rail operators to a much greater extent. Thus the rail operators have much more say over how the rail is used and obviously priorities the more profitable traffic, which in the US is cargo.
So if the US government would wanted to build out cross country passenger rail they would either have to build new tracks, or use eminent domain to take back control of the existing tracks. Both options would be very expensive and wildly unpopular.
Which Europe are you talking about? Europe is a collection of independent counties and what you just mention is all wrong.
Most of the European railway companies have been privatized and there are companies that run the rail network and companies that run the train. Subsidies are not a thing in many of the European countries
If you look at the UK for example, the physical network is publicly owned and maintained by National Rail, whilst the ToCs are (currently) mostly private. That said the ToCs are also going to switch to publicly owned over the next few years.
So if the US government would wanted to build out cross country passenger rail they would either have to build new tracks, or use eminent domain to take back control of the existing tracks. Both options would be very expensive and wildly unpopular.