system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Being such a vast country, how come the US does not have high speed trains to connect major cities?
gpt
Cost and distance.  Building rail infrastructure requires a large investment, and the distance between population centers is huge.  Outside of the North-East, the population density is very low across the US.  

In addition, we have a somewhat-decent network or roads and airlines which cover the majority of transit needs.