First, I assume that "NEC" means North East Corridor which has a "high speed" train on Boston-NYC-WashingtonDC. Second, "relatively cheap fixes: removing sharp curves": You lost me here. That train must be about 20 years old now. If this was so cheap and easy, why not already done?

Hell if I know why it hasn’t already been done. All I’m saying is that the route slows down because of some sharper turns in some areas, and fixing it would be easier than making completely new lines/stations. I’m sure it would be much more expensive than similar projects elsewhere in the world