In many countries one person operation can work on metro systems, but NY is probably about 50 years of investment behind in infrastructure before that's a good idea.
At every station I've ever been to, the boarding is level, and the gap is small.
Many (though not all yet) stations have elevators large enough for a disabled person in a wheelchair.
All buses (operated by the same MTA as the usbway) have a foldable ramp for wheelchairs, used quite routinely.
Platforms can sink and otherwise decay over time. Many of the stations are quite old.
Low platforms, by contrast, are nowhere near the height of the train floor.
> 14th Street–Union Square northbound 4 trains have a 5.5-inch vertical gap, 59th Street–Columbus Circle northbound B trains have a gaping seven-inch horizontal gap, and Times Square–42nd Street eastbound 7 trains have both: a 5.5-inch vertical gap and a five-inch horizontal gap
https://www.curbed.com/2022/10/mta-subway-platform-gaps-laws...