In the 1920s and 1930s certain AC motors had to be 25Hz. I don't know why. But major railroad electrifications like the Pennsylvania, Reading Co., and New Haven used 25 Hz (11,000V). (Former PRR/RDG routes still do to this day.) The electric motors of prewar trains used the 25 Hz. Also, streetcar systems used 600VDC and used rotary converters (an integrated motor-generator set) to convert the power; these also ran off of 25Hz. Modern trains either rectify the AC power to DC or convert it around to AC control.
So, it was common for commercial power plants to supply 25 Hz and continue to supply it for legacy customers. I don't know who supplies today's Amtrak's 25 Hz--whether the power company provides it that way or it has to be converted by the carriers. SEPTA converts theirs, having finally replaced old worn out rotary converters with solid state units.
In the Buffalo area there was an electrified freight switching railway known as Niagara Jct. That probably consumed the 25 Hz. There may have been industrial customers as well.
Note that for many years DC power was provided by commercial utilities. Originally, Edison's power plants supplied DC. There was a big fight between Edison and Westinghouse over DC vs AC. AC won out.