Part of the problem was the steep grades , the LIRR tunnel was below the F train which is a triple-decker tube once it reaches Manhattan. So to have it go from 63rd street to 45th Street and that would have been to steep for US spec'd trains. I'm sure with some modifications an International spec'd train could have handled that. But the FRA required these outrageously heavy trains up until 10yrs ago...so long as the line has PTC installed they can use the European designed trains which are also cheaper to buy. Unfortunately you still see many status quo agencies like the MTA or NJT sticking with the old regulations vs agencies down south or out west going with the new regulations.