why are some electric trains between washington and new york on 25 cycle ac current instread of 60 cycle. ?

Question

Is there something about a lower number of cycles that delivers more power to the motors or makes them more easily controlled

Answer 1

Because that is how the system is set up due to the power supply.

Answer 2

Nowadays, the power system is interconnected, therefore standardized and synchronized. We call it the "power grid".

Not so in the early days of electrification. No interconnection so no standards, and everybody went with what made sense to them. That's no to say there were no grids, but the grids were internal to one company -- the Pennsylvania RR didn't feed power into the IRT subway, etc.

Why don't they switch? Because of the incredible expense and daunting logistics of switching. Trains can be made to run on either frequency (60 vs 25). But for the power distribution equipment - substations, etc. - everything would have to be changed over at once. Of course the railroad would be down (or diesel) for the duration of the changeover and debugging. If Amtrak had a couple billion spare dollars, they sure wouldn't spend it on that.